A hybrid integrated mid-infrared mode-locked quantum cascade laser

Abstract

The present invention discloses a hybrid integrated mid-infrared mode-locked quantum cascade laser, comprising a first chip, a second chip and a substrate heat sink, wherein the first chip and the second chip are hybrid integrated on the substrate heat sink, and the first chip and the second chip work in coupling; the first chip comprises a gain region and a modulation region, wherein the gain region is configured to use the two end faces of the first chip as a resonant cavity under direct current drive to generate a high-power mid-infrared laser, and the modulation region is configured to modulate the gain of the laser under radio frequency drive to generate an active mode-locking effect; the second chip comprises a high-Q cavity, and the mode frequency interval of the high-Q cavity is consistent with the mode frequency interval of the first chip. The present invention can improve the mode-locking stability of the active mode-locked quantum cascade laser, compress the pulse width, and has the advantages of high integration and wide spectral coverage.

Description

Technical Field

[0001] The invention relates to the technical field of lasers, and in particular to a hybrid integrated mid-infrared mode-locked quantum cascade laser. Background Art

[0002] Femtosecond pulse laser is a special laser state with the characteristics of ultra-short duration, ultra-high instantaneous power, ultra-wideband comb spectrum and ultra-high frequency stability. The output wavelengths of most existing femtosecond pulse lasers are visible light and near-infrared; mid-infrared femtosecond pulse lasers are either large in size and low in integration, or have limited wavelength coverage and limited applications. Quantum cascade lasers are currently the most ideal mid-infrared semiconductor lasers, with wavelengths that can cover the entire mid- and far-infrared bands. Based on quantum cascade lasers, it is expected to achieve high-integration, wide-wavelength coverage mid-infrared femtosecond pulse lasers.

[0003] The generation of femtosecond pulse lasers usually relies on mode-locked lasers. However, due to the ultrafast (ps level) gain recovery rate, quantum cascade lasers cannot achieve the most mature passive mode locking, and active mode locking is difficult and has poor mode locking stability. Therefore, the pulse width of the laser pulses generated by the mode-locked quantum cascade laser is relatively large, and femtosecond pulse laser generation cannot be achieved. Summary of the invention

[0004] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a hybrid integrated mid-infrared mode-locked quantum cascade laser. By locking the quantum cascade laser with a passive high-Q cavity and combining it with active mode locking, the mode-locking stability can be improved and the mode-locked pulse width can be compressed, thereby achieving mid-infrared femtosecond pulse laser generation.

[0005] The present disclosure provides a hybrid integrated mid-infrared mode-locked quantum cascade laser, comprising a first chip, a second chip and a substrate heat sink, wherein the first chip and the second chip are hybrid integrated on the substrate heat sink, and the first chip and the second chip are coupled to work;

[0006] The first chip comprises a gain region and a modulation region, wherein the gain region is configured to generate high-power mid-infrared laser by using the end faces of the first chip as a resonant cavity under direct current drive, and the modulation region is configured to modulate the gain of the laser under radio frequency drive to generate an active mode locking effect;

[0007] The second chip includes a high-Q cavity, and a mode frequency interval of the high-Q cavity is consistent with a mode frequency interval of the first chip.

[0008] Optionally, the first chip is an on-chip integrated actively mode-locked mid-infrared quantum cascade laser chip, and the modulation region is configured to achieve high-speed radio frequency modulation at the GHz level.

[0009] Optionally, the electrodes in the modulation area are racket-shaped electrodes.

[0010] Optionally, the first chip includes a first substrate, a lower waveguide layer, a first optical waveguide core layer and an upper waveguide layer arranged in sequence, the substrate is arranged on the base plate heat sink, the gain region and the modulation region are arranged side by side on the upper waveguide layer,

[0011] The gain region comprises a first upper highly doped layer and a first upper electrode layer, wherein the first upper highly doped layer is located between the upper waveguide layer and the first upper electrode layer;

[0012] The modulation region includes a second upper highly doped layer and a second upper electrode layer, wherein the second upper highly doped layer is located between the upper waveguide layer and the second upper electrode layer.

[0013] Optionally, the second chip includes a second substrate, a lower cladding, a second optical waveguide core layer, an upper cladding and an electrode layer arranged in sequence, the second substrate is arranged on the substrate heat sink, and the electrode layer includes a first regulation electrode and a second regulation electrode arranged side by side on the upper cladding.

[0014] Optionally, the first chip and the second chip are efficiently optically coupled.

[0015] Optionally, the first optical waveguide core layer of the first chip is aligned with the second optical waveguide core layer of the second chip, and the mode fields of the first chip and the second chip are matched.

[0016] Optionally, by controlling the magnitude of the direct current of the first control electrode and the second control electrode on the second chip, the coupling phase and the high-Q cavity mode frequency interval between the first chip and the second chip can be regulated.

[0017] Optionally, the first chip and the second chip are hybrid-integrated on the substrate heat sink using high-precision metal bonding technology.

[0018] Optionally, the substrate heat sink is a heat sink made of a material with high thermal conductivity, and the thermal conductivity of the substrate heat sink is greater than 1000 W / (m·K).

[0019] The implementation of the above scheme has the following beneficial effects:

[0020] The present invention integrates the first chip and the second chip on the same substrate heat sink, wherein the first chip is provided with a gain zone and a modulation zone, and the high-Q cavity mode frequency interval of the second chip is consistent with the mode frequency interval of the first chip. When the first chip and the second chip are coupled and work, the gain zone uses the two end faces of the entire first chip as a resonant cavity under direct current drive to generate a high-power mid-infrared laser, and at the same time, the modulation zone modulates the gain of the laser under radio frequency drive to produce an active mode locking effect; the laser mode in the first chip is locked with the high-Q cavity mode of the second chip, which greatly improves the mode locking stability of the mid-infrared mode-locked laser and generates a mid-infrared femtosecond pulse laser.

[0021] Compared with the existing active mode-locked quantum cascade laser, the hybrid integrated mid-infrared mode-locked quantum cascade laser provided by the present disclosure has greatly improved mode-locking stability, effectively compressing the output pulse width to the order of hundreds of femtoseconds. In addition, the quantum cascade laser is a chip-scale mid-infrared femtosecond pulse laser. Compared with the existing mid-infrared femtosecond laser, the quantum cascade laser provided by the present disclosure has the advantages of small size, high integration, and high power density, which greatly expands the application scenarios of mid-infrared femtosecond pulse lasers.

[0022] In addition, the hybrid integrated mid-infrared mode-locked quantum cascade laser provided by the present invention can achieve femtosecond pulse laser output in the wavelength range of 4 microns to 12 microns through wavelength design, which greatly expands the wavelength coverage range of existing mid-infrared femtosecond pulse lasers and can meet the application requirements of more bands.

[0023] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The disclosure of the present invention will become more easily understood with reference to the accompanying drawings. It is easy for those skilled in the art to understand that these drawings are only for illustrative purposes and are not intended to limit the scope of protection of the present invention. In addition, similar numbers in the figures are used to represent similar components, among which:

[0025] Figure 1 is a structural schematic diagram of a hybrid integrated mid-infrared mode-locked quantum cascade laser provided by an embodiment of the present disclosure;

[0026] Figure 2 It is a schematic diagram of the lateral structure of a hybrid integrated mid-infrared mode-locked quantum cascade laser described in the present invention.

[0027] In the figure:

[0028] 1 first chip, 2 second chip, 3 substrate heat sink,

[0029] 11 first substrate, 12 lower waveguide layer, 13 first optical waveguide core layer, 14 upper waveguide layer, 15 gain region, 16 modulation region, 21 second substrate, 22 lower cladding layer, 23 second optical waveguide core layer, 24 upper cladding layer, 25 electrode layer,

[0030] 151 is a first upper highly doped layer, 152 is a first upper electrode layer, 161 is a second upper highly doped layer, 162 is a second upper electrode layer, 251 is a first control electrode, and 252 is a second control electrode. DETAILED DESCRIPTION

[0031] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0032] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0034] In the description of the present invention, it should be noted that the terms "upper", "lower", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, or the positions or positional relationships in which the invention workpiece is usually placed when in use. 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, be constructed and operated in a specific orientation, and therefore cannot be understood as limiting the present invention. In addition, the terms "first", "second", "third", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance. In the description of the present invention, unless otherwise specified, "multiple" means two or more.

[0035] In the description of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "disposed" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0036] In the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may include that the first and second features are in direct contact, or may include that the first and second features are not in direct contact but are in contact through another feature between them. Moreover, a first feature being "above", "above" and "above" a second feature includes that the first feature is directly above and obliquely above the second feature, or simply indicates that the first feature is higher in level than the second feature. A first feature being "below", "below" and "below" a second feature includes that the first feature is directly below and obliquely below the second feature, or simply indicates that the first feature is lower in level than the second feature.

[0037] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and cannot be understood as limiting the present invention.

[0038] The present disclosure provides a hybrid integrated mid-infrared mode-locked quantum cascade laser, see Figure 1The hybrid integrated mid-infrared mode-locked quantum cascade laser includes a first chip 1, a second chip 2 and a substrate heat sink 3; the first chip 1 includes a gain zone 15 driven by direct current and a modulation zone 16 driven by radio frequency, and the second chip 2 includes a split-two waveguide and a coupled ring high-Q cavity; the first chip 1 and the second chip 2 are hybrid integrated on the same substrate heat sink 3 using high-precision metal bonding technology. During operation, the gain zone 15 of the first chip 1, driven by direct current, uses the end faces of the entire first chip 1 as a resonant cavity to generate high-power mid-infrared laser, while the modulation zone 16, driven by radio frequency, modulates the gain of the laser to produce an active mode-locking effect. The first chip 1 and the second chip 2 are optically coupled at the end faces, and the laser generated by the first chip 1 is coupled into the second chip 2, fed back through the ring high-Q cavity, and then returned to the first chip 1. The high-Q cavity included in the second chip 2 is a mid-infrared high-Q cavity, and the high-Q cavity mode frequency interval is close to the mode frequency interval of the first chip 1. By controlling the size of the two direct currents on the second chip 2, the coupling phase between the two chips and the high-Q cavity mode frequency interval can be regulated. When the mode frequency interval of the first chip 1, the RF modulation frequency, and the high-Q cavity mode frequency interval of the second chip 2 are the same, high-stability mode locking is achieved to generate mid-infrared femtosecond pulse laser. The quantum cascade laser provided by the present disclosure has the advantages of high mode locking stability and small pulse width, and provides an optimized mid-infrared femtosecond pulse laser source.

[0039] The first chip 1 is an on-chip integrated active mode-locked mid-infrared quantum cascade laser chip, and the modulation area 16 is configured to achieve GHz-level high-speed radio frequency modulation. Optionally, the electrodes of the modulation area 16 are optimized beat-shaped electrodes to achieve GHz-level high-speed radio frequency modulation.

[0040] The substrate heat sink 3 is a heat sink made of a high thermal conductivity material, such as diamond or composite diamond material, with a thermal conductivity greater than 1000W / (m·K) to achieve efficient heat dissipation of the first chip 1 of the dual-zone quantum cascade laser under high-power output conditions. In a possible implementation, the substrate heat sink 3 is metallized on both sides and patterned on the front side to facilitate powering in different zones. Furthermore, the substrate heat sink 3 is pre-soldered before chip bonding, and In solder or AuSn solder can be used.

[0041] The lateral structure diagram of the hybrid integrated mid-infrared mode-locked quantum cascade laser is shown in Figure 2 As shown, the parts numbered at the beginning of the figure belong to Figure 1 The first chip 1 in the number starting with 2 belongs to Figure 1 The second chip 2, number 3, is Figure 1The substrate heat sink 3 in the embodiment. The first chip 1 and the second chip 2 are hybrid integrated on the substrate heat sink 3. The first chip 1 comprises a first substrate 11, a lower waveguide layer 12, a first optical waveguide core layer 13 and an upper waveguide layer 14 arranged in sequence, the substrate is arranged on the substrate heat sink 3, the gain region 15 and the modulation region 16 are arranged side by side on the upper waveguide layer 14, the gain region 15 comprises a first upper high-doped layer 151 and a first upper electrode layer 152, the first upper high-doped layer 151 is located between the upper waveguide layer 14 and the first upper electrode layer 152; the modulation region 16 comprises a second upper high-doped layer 161 and a second upper electrode layer 162, the second upper high-doped layer 161 is located between the upper waveguide layer 14 and the second upper electrode layer 162. The second chip 2 includes a second substrate 21, a lower cladding 22, a second optical waveguide core layer 23, an upper cladding 24 and an electrode layer 25 arranged in sequence, wherein the second substrate 21 is arranged on the substrate heat sink 3, and the electrode layer 25 includes a first control electrode 251 and a second control electrode 252 arranged side by side on the upper cladding 24. The first optical waveguide core layer 13 of the first chip 1 is aligned with the second optical waveguide core layer 23 of the second chip 2, and the mode fields of the first chip 1 and the second chip 2 are matched, so as to achieve efficient optical coupling between the two chips, and further achieve locking of the laser mode in the first chip 1 with the high-Q cavity in the second chip 2. By controlling the direct current magnitude of the first control electrode 251 and the second control electrode 252 on the second chip 2, the coupling phase and the frequency interval of the high-Q cavity mode between the first chip 1 and the second chip 2 are regulated.

[0042] The invention disclosed herein is described below using a specific embodiment. This embodiment is a hybrid integrated mode-locked quantum cascade laser with a wavelength of 8 μm, comprising a first chip 1 , a second chip 2 and a substrate heat sink 3 .

[0043] The first chip 1 is an InP-based quantum cascade laser, with an active region adopting an 8μm bound state to continuous state structure, an active region period number of 50, an upper highly doped In layer corroded electrical isolation groove, and an upper electrode Au layer also divided into two regions, thereby dividing the first chip 1 into a gain region 15 and a modulation region 16. The length of the gain region 15 is 4.5mm, the length of the modulation region 16 is 1.5mm, and the total length of the first chip 1 is 6mm. During operation, the gain region 15 is driven by direct current, and the end faces of the entire chip are used as a resonant cavity, the cavity length is 6mm, and a high-power mid-infrared laser is generated, and the corresponding cavity mode frequency interval is 7.8GHz. At the same time, the modulation region 16 modulates the gain of the laser under RF drive, and the modulation frequency is strictly equal to the mode frequency interval of the first chip 1, producing an active mode locking effect.

[0044] The second chip 2 is a Si-based Ge waveguide passive feedback chip, which contains a high-Q cavity with a Q value greater than 1×106, and the high-Q cavity mode frequency interval is also about 7.8GHz. During operation, the feedback phase and the high-Q cavity mode frequency interval can be precisely controlled by adjusting the current on the two electrodes on the second chip 2, so that the high-Q cavity mode frequency interval is strictly equal to the mode frequency interval of the first chip 1.

[0045] The substrate heat sink 3 is a copper-diamond composite heat sink with prefabricated AuSn solder, and the thermal conductivity is greater than 1000W / (m·K). The first chip 1 and the second chip 2 are hybrid integrated on the substrate heat sink 3 using high-precision metal bonding technology. The mode fields of the first chip 1 and the second chip 2 are matched, and the waveguide cores are strictly aligned, so that the two chips are efficiently optically coupled, and the laser mode of the first chip 1 is locked with the high Q mode of the second chip 2, which greatly improves the mode-locking stability of the mode-locked quantum cascade laser.

[0046] In this embodiment, the average power of the laser output is 0.9W, the repetition frequency is 7.8GHz, the mode-locked wavelength covers a range of 7.7μm–8.3μm, the pulse width is 0.5 femtoseconds, and the pulse peak power is as high as 230W.

[0047] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A hybrid integrated mid-infrared mode-locked quantum cascade laser, characterized in that: It comprises a first chip, a second chip and a substrate heat sink, wherein the first chip and the second chip are hybrid-integrated on the substrate heat sink, and the first chip and the second chip are coupled to work; The first chip comprises a gain region and a modulation region, wherein the gain region is configured to generate high-power mid-infrared laser by using the end faces of the first chip as a resonant cavity under direct current drive, and the modulation region is configured to modulate the gain of the laser under radio frequency drive to generate an active mode locking effect; The second chip comprises a high-Q cavity, and the mode frequency interval of the high-Q cavity is consistent with the mode frequency interval of the first chip; The first chip comprises a first substrate, a lower waveguide layer, a first optical waveguide core layer and an upper waveguide layer which are arranged in sequence, the substrate is arranged on the base plate heat sink, the gain region and the modulation region are arranged side by side on the upper waveguide layer, The gain region comprises a first upper highly doped layer and a first upper electrode layer, wherein the first upper highly doped layer is located between the upper waveguide layer and the first upper electrode layer; The modulation region includes a second upper highly doped layer and a second upper electrode layer, wherein the second upper highly doped layer is located between the upper waveguide layer and the second upper electrode layer.

2. The hybrid integrated mid-infrared mode-locked quantum cascade laser according to claim 1, characterized in that: The first chip is an on-chip integrated actively mode-locked mid-infrared quantum cascade laser chip, and the modulation area is configured to achieve high-speed radio frequency modulation at the GHz level.

3. The hybrid integrated mid-infrared mode-locked quantum cascade laser according to claim 2, characterized in that: The electrodes in the modulation area are beat-shaped electrodes.

4. The hybrid integrated mid-infrared mode-locked quantum cascade laser according to claim 1, characterized in that: The second chip includes a second substrate, a lower cladding, a second optical waveguide core layer, an upper cladding and an electrode layer arranged in sequence, the second substrate is arranged on the base plate heat sink, and the electrode layer includes a first control electrode and a second control electrode arranged side by side on the upper cladding.

5. The hybrid integrated mid-infrared mode-locked quantum cascade laser according to claim 1 or 4, characterized in that: The first chip and the second chip are efficiently optically coupled.

6. The hybrid integrated mid-infrared mode-locked quantum cascade laser according to claim 5, characterized in that: The first optical waveguide core layer of the first chip is aligned with the second optical waveguide core layer of the second chip, and the mode fields of the first chip and the second chip are matched.

7. The hybrid integrated mid-infrared mode-locked quantum cascade laser according to claim 6, characterized in that: By controlling the magnitude of the direct current of the first control electrode and the second control electrode on the second chip, the coupling phase and the high-Q cavity mode frequency interval between the first chip and the second chip can be regulated.

8. The hybrid integrated mid-infrared mode-locked quantum cascade laser according to claim 1, characterized in that: The first chip and the second chip are hybrid-integrated on the substrate heat sink by using high-precision metal bonding technology.

9. The hybrid integrated mid-infrared mode-locked quantum cascade laser according to claim 1, characterized in that: The substrate heat sink is a heat sink made of a material with high thermal conductivity, and the thermal conductivity of the substrate heat sink is greater than 1000 W / (m·K).

Images