A scanning laser light source for FMCW

Abstract

The present invention relates to the field of frequency modulated continuous laser technology, and in particular to a frequency modulated continuous laser light source, which includes a tunable narrow line width laser, a first semiconductor optical amplifier, a modulator, a wavelength selective reflector and an optical phased array in sequence according to the light output direction. The present invention uses extra-cavity modulation frequency sweeping without affecting the light source correlation, and theoretically only generates two narrow line width longitudinal mode components of light, and does not generate other high-order harmonic components. Through wavelength selection, a scanning laser source with narrow line width, wide range wavelength tunability, and high-speed linear frequency sweeping can be realized, and the scanning speed is fast.

Description

Technical Field

[0001] The invention relates to the technical field of frequency modulated continuous laser technology, and in particular to a scanning laser light source for FMCW. Background Art

[0002] Frequency modulated continuous wave (FMCW) laser technology is a laser technology whose frequency changes with time. It has broad application prospects in optical communications, optical sensing, lidar, and imaging. The current frequency modulated continuous wave laser is realized through direct modulation technology and external modulation technology.

[0003] Direct modulation technology is achieved through electrically modulated lasers or external cavity modulated lasers. Electrically modulated lasers use current-tuned semiconductor lasers to change the output wavelength by changing the laser's injected current. There is no need for complex mechanical tuning mechanisms, the package size is very small, and the structure is compact. However, the laser frequency and modulation current are nonlinearly related. At the same time, current-tuned semiconductor lasers have serious frequency modulation nonlinearity problems, the tuning accuracy and tuning speed are difficult to control, and the wavelength tuning range is small. Although the external cavity laser has a larger wavelength tuning range, it is larger in size and weight, has poor seismic resistance, slow frequency scanning speed, and is expensive. Therefore, the current direct modulation technology has a limited scope of use.

[0004] External modulation technology is implemented through electro-optic modulators or semiconductor electro-absorption modulators (EAM). Electro-optic modulators are based on electro-optic crystals such as lithium niobate and GaAs, and semiconductor electro-absorption modulators are based on the quantum confinement effect of semiconductor quantum wells. Since the light field confinement factor r is determined by the waveguide structure of the EAM, the wider the waveguide width, the larger the confinement factor, and the slower the response speed of the EAM; the higher the waveguide height, the larger the confinement factor, but it does not affect the modulation speed. The frequency chirp characteristics of the electro-optic modulator can be zero or even negative, and it is widely used in long-distance high-speed optical communication systems, lidar, fiber optic sensing and other fields.

[0005] At present, the use of electro-optic modulators or semiconductor electro-absorption modulators to generate FMCW optical signals requires the use of I / Q single-sideband modulation technology. The modulation process is as follows: After loading a continuous frequency modulation signal on the modulator, the laser passing through the modulator will generate several harmonic components containing the continuous frequency modulation signal, and the frequency interval of each harmonic is f. By properly biasing the modulator to make it work at the maximum or minimum value of the transmission function and filtering out unnecessary harmonic components, the FMCW light source can be realized. The intensity modulator requires a DC bias. When the DC bias drifts, the intensity modulator deviates from the maximum and minimum values ​​of the transmission function. At this time, it is difficult to suppress odd and even harmonics, resulting in a decrease in the sound characteristics. With phase modulation, there is no need to use a DC bias, but it is also necessary to suppress high-order harmonics.

[0006] In addition, the power of the harmonic component is closely related to the modulation depth. In order to suppress unnecessary harmonics and obtain ideal output power, the modulation depth needs to be optimized. It can be seen that the above method of realizing FMCW modulation by generating harmonic components containing continuous frequency modulation signals needs to suppress unnecessary high-order harmonic components, the modulation control circuit is more complicated, and the noise is more difficult to suppress. Summary of the invention

[0007] In order to improve the above technical problems, the present invention provides a frequency modulated continuous laser light source, which includes a tunable narrow linewidth laser, a first semiconductor optical amplifier (semiconductor optical amplifier, SOA), a modulator, a wavelength selective reflector and an optical phased array (Optical Phased Array, OPA) in sequence according to the light output direction.

[0008] (hereinafter, the first semiconductor optical amplifier is referred to as the first SOA, and the optical phased array is referred to as OPA)

[0009] According to an embodiment of the present invention, an optical isolator and a coupling waveguide are provided between the tunable narrow linewidth laser and the first SOA, and more preferably, the tunable narrow linewidth laser and the first SOA are electrically isolated;

[0010] Preferably, an optical isolator and a coupling waveguide are provided between the first SOA and the modulator, and more preferably, the first SOA and the modulator are electrically isolated;

[0011] Preferably, an optical isolator and a coupling waveguide are provided between the modulator and the wavelength selective reflector, and more preferably, the modulator and the wavelength selective reflector are electrically isolated;

[0012] Preferably, an optical isolator and a coupling waveguide are provided between the wavelength selective reflector and the OPA, and more preferably, the wavelength selective reflector and the OPA are electrically isolated.

[0013] According to an embodiment of the present invention, a second semiconductor optical amplifier (second SOA) is provided between the wavelength selective reflector and the OPA.

[0014] According to an embodiment of the present invention, the tunable narrow linewidth laser comprises a first epitaxial structure, a first ridge waveguide is grown on the first epitaxial structure, and the first ridge waveguide has a width of 1 to 4 μm and a height of 1 to 2 μm.

[0015] Preferably, the first epitaxial structure includes a substrate, a buffer layer, a lower confinement layer, a lower waveguide layer, an active layer, an upper waveguide layer, an upper confinement layer, and a contact layer which are arranged in sequence from bottom to top.

[0016] According to an embodiment of the present invention, the active layer comprises several layers of In x Ga 1-x As y P 1-y A quantum well, wherein the number of layers of the quantum well is ≥3 layers, preferably ≥4 layers, for example, 4 layers;

[0017] The value range of x is 0-1, and the value range of y is 0-1; the bandgap width E is determined according to the wavelength of the designed laser g , the values ​​of x and y must satisfy formula 4:

[0018] E g =2.75-1.33y-1.4x+0.33xy-(0.758-0.28y)x(1-x)-(0.21-0.109x)y(1-y)...Formula 4;

[0019] For example, the In x Ga 1-x As y P 1-y Quantum well is In 0.557 Ga 0.443 As 0.95 P 0.05 Quantum well, preferably, the In 0.557 Ga 0.443 As 0.95 P 0.05 The thickness of the quantum well is 6 nm.

[0020] Preferably, adjacent to the In x Ga 1-x As y P 1-y There is a potential barrier between the quantum wells, preferably, the potential barrier is In 0.738 Ga 0.262 As 0.568 P 0.432 Preferably, the thickness of the barrier is 10 nm.

[0021] Preferably, the substrate is N + -InP substrate;

[0022] Preferably, the buffer layer is N + -InP, with a thickness of 0.5-1 μm; preferably, the buffer layer has a thickness of 0.6-0.8 μm.

[0023] The lower limiting layer is N + -InP, with a thickness of 1-2 μm; preferably, the thickness of the upper limiting layer is 0.4-0.6 μm.

[0024] Preferably, the lower waveguide layer is InGaAsP with a thickness of 0.1-0.2 μm; preferably, the thickness of the lower confinement layer is 0.7-0.17 μm.

[0025] The upper waveguide layer is InGaAsP with a thickness of 0.1-0.2 μm; preferably, the thickness of the lower confinement layer is 0.7-0.17 μm.

[0026] The upper limiting layer is N-InP, and has a thickness of 1 to 2.5 μm; preferably, the thickness of the upper limiting layer is 1.4-2 μm.

[0027] The contact layer is P + - InGaAs, with a thickness of 0.1-0.4 μm. Preferably, the contact layer has a thickness of 0.2-0.3 μm.

[0028] According to an embodiment of the present invention, the tunable narrow linewidth laser includes adjacent laser gain regions and phase shift regions. If the laser gain region is the final light-emitting region, at least one DBR (distributed Bragg reflector) is provided on the light-emitting side of the laser gain region. More preferably, at least one DBR is provided on the non-light-emitting side of the phase shift region.

[0029] If the phase shift region is the final light-emitting region, at least one DBR is provided on the light-emitting side of the phase shift region; more preferably, at least one DBR is provided on the non-light-emitting side of the laser gain region.

[0030] Preferably, at least one DBR may be provided between the laser gain region and the phase shift region;

[0031] Preferably, the phase shift region can achieve wavelength tuning; the laser gain region achieves laser output; both are plated with electrodes on the contact layer of the first epitaxial structure for injecting current, and electrical isolation is achieved between the two.

[0032] According to an embodiment of the present invention, the DBR is a passive grating structure, the DBR is arranged on the top of the first epitaxial layer structure, the gap between adjacent DBRs is a grating groove, the depth of the grating groove is 1 to 3 μm, and the bottom of the grating groove is located at the upper waveguide layer or the upper limiting layer of the first epitaxial structure; an electrical insulating layer and a metal electrode are arranged on the grating groove; preferably, the electrical insulating layer is made of SiO2 with a thickness of 100 to 200 nm; preferably, the thickness of the metal electrode is 100 to 300 nm.

[0033] According to an embodiment of the present invention, the first SOA has a second epitaxial structure, and the second epitaxial structure is the same as the first epitaxial structure; preferably, an electrode is provided on the contact layer of the second epitaxial structure for injecting current.

[0034] Preferably, the second epitaxial structure and the tunable narrow linewidth laser are electrically isolated;

[0035] Preferably, the first SOA is connected to the tunable narrow linewidth laser via a coupling waveguide, and the coupling waveguide comprises a tilted waveguide or a straight waveguide with an end facet beveled.

[0036] Preferably, the coupling waveguide is a heterogeneous collection of silicon waveguide and group III, V materials, which can achieve low-loss coupling of semiconductor optical amplifiers. More preferably, the coupling waveguide includes at least one of a silicon waveguide, a silicon nitride waveguide, and a lithium niobate thin film waveguide.

[0037] According to an embodiment of the present invention, the modulator is any one of an intensity modulator, an electroabsorption modulator or a lithium niobate modulator, or a combination of two or more thereof, preferably an electroabsorption modulator.

[0038] Preferably, the electro-absorption modulator comprises a third epitaxial structure and a ridge waveguide structure, and the ridge waveguide structure is grown on the third epitaxial structure.

[0039] An electrode is plated on the contact layer of the third epitaxial structure for injecting a modulated current. Preferably, the third epitaxial structure is the same as or different from the first epitaxial structure; for example, the number of quantum wells and potential barriers of the third epitaxial structure is different from that of the first epitaxial structure. As an example, the third epitaxial layer includes 7 quantum wells and 6 potential barriers.

[0040] Preferably, the ridge waveguide structure is a deeply etched waveguide structure, for example, the quantum well of the ridge waveguide structure is etched through; preferably, the length of the ridge waveguide structure is 150-250 μm, the ridge height is 1-3 μm, and the ridge width is 2-4 μm.

[0041] Preferably, the ridge waveguide structure is made of a lithium niobate waveguide, and the lithium niobate waveguide includes a lithium niobate thin film waveguide.

[0042] At present, etching low-loss ridge waveguides on lithium niobate films has been achieved. The modulators produced have much better modulation efficiency and speed than the modulators made of the corresponding bulk materials. The integrated performance of this lithium niobate waveguide sheet is better than that of the intensity modulator made of lithium niobate bulk material.

[0043] According to an embodiment of the present invention, the optical phased array includes a waveguide array, a coupling waveguide, a beam splitter and an electrode, the coupling waveguide is used to couple light into the beam splitter, the beam splitter is connected to the coupling waveguide to form a branch signal, the waveguide array receives the branch signal, the electrode is coated on the waveguide array to form a phase tuning region, and the phase tuning region realizes the change of the radiation direction of the optical signal under the control of the phase tuning control circuit.

[0044] The waveguide array includes a plurality of waveguides, and the waveguides are made of silicon, silicon oxide, silicon nitride, GaAs, InP, InGaAs or InGaAsP.

[0045] Preferably, when it is a silicon-based waveguide, the core width of the waveguide in the waveguide array is a=0.2~0.6μm, the height is h=0.15~0.35μm, the length is L=50~100μm, the period d of the waveguide array is 0.6~1.5μm, and the number of waveguides in the waveguide array is greater than 5.

[0046] When it is a GaAs waveguide, the width of the waveguide core layer in the waveguide array is a=1.5-4 μm, the height is h=0.8-1.8 μm, the length is L=50-100 μm, and the number of waveguides in the waveguide array is greater than 5.

[0047] According to an embodiment of the present invention, the wavelength selective reflector comprises an incident waveguide and an exit waveguide which are arranged opposite to each other, and at least one microcavity is arranged between the incident waveguide and the exit waveguide.

[0048] Preferably, at least two microcavities are arranged between the incident waveguide and the exit waveguide. Preferably, the sizes and shapes of the different microcavities are the same or different. More preferably, the microcavity is annular, disc-shaped, spherical or square, for example, an annular cavity with an outer diameter of 20 to 100 μm and an inner diameter of 2 to 90 μm.

[0049] Preferably, one end of the incident waveguide is connected to the modulator, and more preferably, the other end is connected to the electro-absorption region; preferably, the incident end of the output waveguide is connected to the electro-absorption region, and the output end is connected to the optical array OPA or the second SOA.

[0050] Preferably, the length of the output waveguide and the input waveguide is 100-200 μm, the height is 0.5-3 μm, and the width is 1-6 μm. The length, height, and width of the output waveguide and the input waveguide are the same or different.

[0051] Preferably, there is a certain gap between the incident waveguide, the output waveguide and the microcavity, and the width of the gap is 0.5-10 μm.

[0052] Preferably, the wavelength selective reflector is made of silicon, silicon oxide, silicon nitride, InP, InGaAsP, GaAs, InGaAs, or an organic semiconductor.

[0053] Preferably, the wavelength selective reflector can achieve separation of two optical longitudinal mode signals with a frequency interval of more than 5 GHz.

[0054] Preferably, the lowest frequency of the FMCW modulation signal is 1 / 2 of the 43dB bandwidth of the wavelength selective reflector, and the FMCW modulation bandwidth is consistent with the 43dB bandwidth of the wavelength selective reflector.

[0055] As an example, the wavelength selective reflector includes two single-mode optical fibers: an incident fused-cone optical fiber and an exit fused-cone optical fiber, the distance between the fused-cone optical fiber and the microcavity is 0.5 to 10 μm; the microcavity is a spherical cavity with a diameter of 10 to 100 μm; one end of the incident optical fiber is connected to the modulator, and the other end is connected to the electric absorption zone; the exit end of the exit optical fiber is connected to the optical array OPA or the second SOA, and the incident end is connected to the electric absorption zone.

[0056] The working principle and process of the laser light source are as follows: the narrow-linewidth laser emits a narrow-linewidth laser, and the electric field intensity E0 of the narrow-linewidth laser is: E0=A0exp(-iω0t+θ0), where ω is the angular frequency of the central wavelength of the laser, A is the amplitude, and θ0 is the initial phase.

[0057] The narrow line width laser increases its output power after passing through the semiconductor optical amplifier and enters the intensity modulator. If the external intensity modulated FMCW signal of the intensity modulator is cos(-ωt+rv 2 t); then the outgoing signal strength is:

[0058] E=Acos(-ωt+rv 2 t)exp(-iω0t+θ0);

[0059] It can be expressed as formula 1:

[0060] 2E=Aexp(-iω0t-iωt+irv 2 t+θ0)+Aexp(-iω0t+iωt-irv 2 t+θ0)……Formula 1

[0061] The outgoing signal is wavelength-selected after passing through the wavelength selective reflector, so that signals with different wavelengths become two beams of light with different propagation directions, as shown in Formula 2 and Formula 3:

[0062] E1=Aexp(-iω0t-iωt+irv 2 t+θ0)……Formula 2

[0063] E2=Aexp(iω0t-iωt+irv 2 t-θ0)……Formula 3

[0064] One of the signals is selected and passed through another amplifying semiconductor optical amplifier, and then output through the optical OPA array.

[0065] As an example, a scanning laser light source for FMCW includes a narrow-line fiber laser, a fiber amplifier, a fiber modulator, a fiber wavelength selector, and an optical OPA array, wherein a fiber isolator is provided between any two adjacent components of the narrow-line fiber laser, the fiber amplifier, the fiber modulator, the fiber wavelength selector, and the optical OPA array;

[0066] An EDFA amplifier is arranged between the wavelength selective reflector and the optical fiber phased array;

[0067] The optical fiber modulator is an intensity modulator, such as an electro-absorption modulator or a lithium niobate MZ modulator.

[0068] The wavelength selective reflector 4 includes two single-mode optical fibers, one is an incident melt-cone optical fiber, and the other is an exit melt-cone optical fiber. The distance between the melt-cone optical fiber and the microcavity is 0.5 to 10 μm; the microcavity is a spherical cavity with a diameter of 10 to 100 μm; one end of the incident optical fiber is connected to the modulator 3, and the other end is connected to the electric absorption zone; the exit end of the exit optical fiber is connected to the optical OPA array 5 or the optical fiber amplifier 2, and the other end is connected to the electric absorption zone.

[0069] Beneficial Effects

[0070] The scanning laser light source for FMCW provided by the present invention is composed of a narrow line width laser and an intensity modulator. Through the external cavity modulation frequency sweep, the correlation of the light source is not affected. In theory, only two narrow line width longitudinal mode components are generated, and no other high-order harmonic components are generated. Through wavelength selection, a scanning laser source with narrow line width, wide range wavelength tuning, and high-speed linear frequency sweep can be realized, and the scanning speed is fast.

[0071] The wavelength selective reflector of the present invention comprises an incident waveguide, an output waveguide and a microcavity structure, wherein the microcavity structure can effectively suppress the dual longitudinal mode phenomenon occurring after intensity modulation; an electric absorption region is connected to the output ends of the incident waveguide and the output waveguide to eliminate unnecessary feedback; and the influence on the narrow line width laser and the modulator is reduced.

[0072] By heterogeneous integration, the advantages of the modulator, such as fast modulation speed, good linearity and no effect of laser linewidth on extra-cavity tuning, are combined with narrow linewidth lasers to meet the needs of long-distance and high-speed ranging.

[0073] On-chip heterogeneous integration of narrow-linewidth lasers, the first semiconductor optical amplifiers, modulators, wavelength-selective reflectors, and optical phased arrays enables greater material selectivity and compromised device performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0074] Figure 1 It is a structural block diagram of the on-chip frequency modulated continuous laser light source in Example 1;

[0075] Figure 2 It is a schematic diagram of the structure of a tunable narrow linewidth laser;

[0076] Figure 3 is a schematic diagram of the structure of the intensity modulator;

[0077] Figure 4 is a schematic structural diagram of a first epitaxial structure;

[0078] Figure 5 Schematic diagram of the ridge waveguide structure of the electro-absorption modulator;

[0079] Figure 6 Schematic diagram of separating optical signals for wavelength selective reflectors;

[0080] Figure 7 Schematic diagram of the structure of an optical phased array.

[0081] Among them, 1-tunable narrow linewidth laser, 2-semiconductor SOA amplifier, 3-modulator, 31-incident waveguide, 32-exit waveguide, 33-microcavity, 34-electric absorption region, 4-wavelength selective reflector, 5-optical OPA array, 51-optical waveguide array, 52-beam splitter, 53-coupled waveguide, 54-electrode, 6-laser gain region, 7-distributed Bragg reflector, 8-phase shift region.

[0082] 21 - substrate, 22 - buffer layer, 23 - lower confinement layer, 24 - lower waveguide layer, 25 - active layer, 26 - upper waveguide layer, 27 - upper confinement layer, 28 - contact layer. DETAILED DESCRIPTION

[0083] The following will be further described in detail with reference to specific examples of the general formula compound of the present invention and its preparation method and application. It should be understood that the following examples are only for exemplary description and explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies realized based on the above content of the present invention are included in the scope that the present invention is intended to protect.

[0084] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0085] Example 1

[0086] See also Figure 1 As shown, a scanning laser light source for FMCW includes, in order according to the light output direction, a tunable narrow linewidth laser 1, a semiconductor SOA amplifier 2, a modulator 3, a wavelength selective reflector 4 and an optical OPA array 5.

[0087] Among the tunable narrow linewidth laser 1, the semiconductor SOA amplifier 2, the modulator 3, the wavelength selective reflector 4 and the optical OPA array 5, an optical isolator and a coupling waveguide are arranged between any two adjacent components, and any adjacent components above are electrically isolated.

[0088] Another semiconductor SOA amplifier is arranged between the wavelength selective reflector 4 and the optical OPA array 5 .

[0089] See also Figure 2 As shown, the tunable narrow linewidth laser 1 includes a laser gain region 6, a distributed Bragg reflector (DBR) 7 and a phase shift region 8. The relative positions of the structured laser gain region 6 and the phase shift region 8 can be interchanged left and right; there is at least one DBR 7 on the light emitting side of the structured laser gain region 6 and the phase shift region 8; there can be a DBR 7 between the structured laser gain region 6 and the phase shift region 8; and there can be a DBR 7 on the non-light emitting surface of the structured laser gain region 6 and the phase shift region 8.

[0090] The phase shift region 8 can achieve wavelength tuning; the laser gain region 6 realizes laser output; both are plated with electrodes on the contact layer of the epitaxial structure for injecting current, and electrical isolation is achieved between the two.

[0091] The modulator 3 is an intensity modulator, such as an electro-absorption modulator, a lithium niobate modulator, or other types of modulators that can achieve intensity modulation and their combined structures.

[0092] See also Figure 3 As shown, the wavelength selective reflector 4 can effectively suppress the dual longitudinal mode phenomenon that occurs after the modulator 3; the wavelength selective reflector 4 adopts microcavity filtering technology, including Figure 3 The two parallel waveguides shown in the figure are: an incident waveguide 31 and an output waveguide 32. One end of the incident waveguide 31 is connected to the modulator 3, and the other end is connected to the electric absorption region 34 to eliminate unnecessary feedback; the output end of the output waveguide 32 is connected to the optical OPA array 5 or the second semiconductor SOA amplifier, and the other end is connected to the electric absorption region 34 to eliminate unnecessary feedback.

[0093] There is a microcavity 33 between the incident waveguide 31 and the output waveguide 32; there is at least one microcavity 33, and when there are multiple microcavities 33, their sizes can be different; the microcavity 33 can be designed in different shapes and sizes as needed, and can be annular, disc, spherical, square, etc.

[0094] The material used for the wavelength selective reflector 4 can be silicon and its oxide or nitride, or InP, InGaAsP, GaAs, InGaAs, or organic semiconductors, etc. It can achieve separation of two optical longitudinal mode signals with a frequency interval of more than 5 GHz.

[0095] The lowest frequency of the FMCW modulation signal is 1 / 2 of the 43dB bandwidth of the wavelength selective reflector, and the FMCW modulation bandwidth is consistent with the 43dB bandwidth of the wavelength selective reflector.

[0096] The length of the output waveguide 32 and the input waveguide 31 is 100-200 μm, the height is 0.5-3 μm, and the width is 1-6 μm; the parameters of the two can be consistent or inconsistent. The microcavity 33 is a ring cavity with an outer diameter of 20-100 μm and an inner diameter of 2-90 μm; there is a gap of a certain width of 0.5-10 μm between the input waveguide 31 and the output waveguide 32 and the microdisk 33; the structure of the electro-absorption region 34 is the same as the gain region 6 of the tunable narrow linewidth laser 1. When a voltage is applied, the voltage bias of the electro-absorption region 34 is opposite to that of the laser gain region 6.

[0097] The specific working principle and process of the structure are as follows: the narrow line width laser emitted by the narrow line width laser 1 has an electric field intensity E0 which can be expressed as: E0 = A0exp(-iω0t+θ0), where ω is the angular frequency of the laser center wavelength, A is the amplitude, and θ0 is the initial phase; after passing through the semiconductor SOA amplifier 2, the output power increases, and then passes through the intensity modulator 3. If the intensity modulator 3 is externally modulated with an intensity modulator FMCW signal of cos(-ωt+rv 2 t); then the outgoing signal strength is:

[0098] E=Acos(-ωt+rv 2 t)exp(-iω0t+θ0);

[0099] It can be expressed as:

[0100] 2E=Aexp(-iω0t-iωt+irv 2 t+θ0)+Aexp(-iω0t+iωt-irv 2 t+θ0);

[0101] After passing through the wavelength selective reflector 4, wavelength selection is performed, so that the signal becomes:

[0102] E1=Aexp(-iω0t-iωt+irv 2 t+θ0)

[0103] or:

[0104] E2=Aexp(-iω0t+iωt-irv 2 t+θ0)

[0105] After passing through the amplifying semiconductor second SOA amplifier, it is output through the optical OPA array 5.

[0106] For the laser source with an output wavelength of 1550nm, an InP / InGaAsP material system is used, and the substrate is InP.

[0107] For the laser source with an output wavelength of 850nm, a GaAs / InGaAs material system is used, and the substrate is GaAs.

[0108] The material system for integrating the light source may be different material systems such as InGaAsP / InP system, InGaAs / GaAs system, InGaAsAl / GaAs system, etc.

[0109] See also Figure 4 As shown, the epitaxial structure of the narrow linewidth laser 1 is arranged in order from bottom to top: a substrate 21, a buffer layer 22, a lower confinement layer 23, a lower waveguide layer 24, an active layer 25, an upper waveguide layer 26, an upper confinement layer 27, and a contact layer 28;

[0110] The active layer 25 of the narrow linewidth laser 1 includes several layers of In x Ga 1-x As y P 1-y Quantum well, the number of layers of the quantum well is ≥3, preferably, the number of potential barriers is ≥2, for example, the number of layers of the quantum well is 6, and the number of potential barriers is 5;

[0111] The value range of x is 0-1, and the value range of y is 0-1; the bandgap width E is determined according to the wavelength of the designed narrow linewidth laser 1 g , the values ​​of x and y must satisfy the formula:

[0112] E g =2.75-1.33y-1.4x+0.33xy-(0.758-0.28y)x(1-x)-(0.21-0.109x)y(1-y);

[0113] For example, the In x Ga 1-x As y P 1-y Quantum well is In 0.76 Ga 0.24 As 0.81 P 0.19 Quantum well, preferably, the quantum well In 0.77 Ga 0.23 As 0.8 P 02 , with a thickness of 6nm.

[0114] Adjacent two x Ga 1-x As y P 1-yThere is a potential barrier between the quantum wells, and the potential barrier is In 0.72 Ga 0.28 As 0.6 P 0.4 , thickness is 10nm.

[0115] The substrate is N + -InP substrate, the buffer layer is N + -InP, with a thickness of 0.5 to 1 μm; the lower limiting layer N + -InP layer, with a thickness of 1 to 2 μm, the lower waveguide layer is InGaAsP, with a thickness of 0.1 to 0.2 μm; the upper waveguide layer is InGaAsP, with a thickness of 0.1 to 0.2 μm; the upper confinement layer is P-InP, with a thickness of 1 to 2.5 μm; the contact layer is P + -InGaAs, thickness is 0.1~0.4μm.

[0116] The ridge waveguide of the narrow linewidth laser 1 has a width of 1 to 4 μm and a height of 1 to 2 μm.

[0117] DBR is a passive grating structure, with grating grooves between adjacent DBRs. The depth of the grating grooves is 1 to 3 μm, which can penetrate into the upper waveguide layer and the upper confinement layer, but the depth does not reach the active area and does not damage the active area. The grating grooves can introduce a 100 to 200 nm SiO2 electrical insulation layer and a 100 to 300 nm metal electrode. The grating can use a high-order grating, and the width is determined by the order of the selected grating.

[0118] The epitaxial structure of the semiconductor SOA2 is the same as that of the narrow linewidth laser 1, and can also be supplemented or replaced with a material having optimized light amplification characteristics. An electrode is plated on the contact layer of the epitaxial structure of the semiconductor SOA2 for injecting current, and the epitaxial structure of the semiconductor SOA2 is electrically isolated from the narrow linewidth laser 1. The coupling waveguide of the semiconductor SOA 2 and the laser 1 adopts an inclined waveguide, or a straight waveguide is beveled.

[0119] Heterogeneous integration of silicon waveguides and III, V group material waveguides can achieve low-loss coupling of SOA. The III, V group material waveguides include at least one of silicon waveguides, silicon nitride waveguides and lithium niobate thin film waveguides.

[0120] See also Figure 5 As shown, the modulator 3 is an electro-absorption modulator (EMA), which includes an epitaxial structure and a ridge waveguide structure. The ridge waveguide structure needs to further etch the quantum well to form a deeply etched waveguide structure; the length of the ridge waveguide structure is 150 to 250 μm, the ridge height is 1 to 3 μm, and the ridge width is 2 to 4 μm.

[0121] The electroabsorption modulator is plated with electrodes on the contact layer of the epitaxial structure for injecting modulation current. Its epitaxial structure can be the same as or different from the epitaxial structure of the narrow linewidth laser 1; for example, the number of quantum well and barrier layers can be different, with 7 quantum well layers and 6 barrier layers.

[0122] The modulator 3 can also be made of a lithium niobate waveguide, wherein the lithium niobate waveguide can include a lithium niobate thin film waveguide. At present, etching a low-loss ridge waveguide on a lithium niobate thin film has been achieved. The modulation efficiency and speed of the modulator produced are greatly superior to those of the modulator made of its corresponding bulk material. The integrated performance of the lithium niobate waveguide chip is better than that of the intensity modulator made of lithium niobate bulk material.

[0123] See also Figure 7 As shown, the optical OPA array 5 is composed of an optical waveguide array 51, a coupling waveguide 53, a beam splitter 52, and an electrode 54. The material of the optical waveguide array 51 can be silicon or its oxide and nitride, or GaAs, InP, InGaAs, InGaAsP and other materials. For silicon-based waveguides: the core layer width a of the optical waveguide array 51 is 0.2-0.6 μm, the height h is 0.15-0.35 μm, the length L is 50-100 μm, the period of the optical waveguide array 51 is 0.6-1.5 μm, and the number of waveguides N is greater than 5. The GaAs optical waveguide array 51 selects a core layer width a=1.5~4μm, a height h=0.8~1.8μm, a length L=50~100μm, and a waveguide number N greater than 5. The upper cladding of the optical waveguide array 51 is GaAs of AlGaAs. Under the excitation of a single light source mode, the light field transmission diagram when the array period d is 1.5μm~4μm and the transmission loss diagram of the waveguide where the incident light is located are simulated.

[0124] Silicon-based waveguides adjust the refractive index based on the thermo-optic effect to achieve phased array scanning, while GaAs, lithium niobate and other waveguide arrays adjust the refractive index based on the electro-optic effect to achieve phased array scanning.

[0125] Example 2

[0126] A scanning laser light source (all-fiber type) for FMCW, comprising a narrow-line fiber laser 1, a fiber amplifier 2, a fiber modulator 3, a fiber wavelength selector 4 and an optical OPA array 5, wherein a fiber isolator 6 is provided between any two adjacent components of the narrow-line fiber laser 1, the fiber amplifier 2, the fiber modulator 3, the fiber wavelength selector 4 and the optical OPA array 5;

[0127] An EDFA amplifier 2 is provided between the wavelength selective reflector 4 and the optical fiber phased array 5;

[0128] The optical fiber modulator 3 is an intensity modulator, such as an electro-absorption modulator or a lithium niobate MZ modulator.

[0129] The wavelength selective reflector 4 can effectively suppress the dual longitudinal mode phenomenon appearing after the modulator 3; the wavelength selective reflector 4 adopts microcavity filtering technology and includes two single-mode optical fibers, one is an incident melt-cone optical fiber, and the other is an exit melt-cone optical fiber, and the distance between the melt-cone optical fiber and the microcavity is 0.5 to 10 μm; the microcavity is a spherical cavity with a diameter of 10 to 100 μm; one end of the incident optical fiber is connected to the modulator 3, and the other end can be connected to the electric absorption zone to eliminate unnecessary feedback; the exit end of the exit optical fiber is connected to the optical OPA array 5 or the optical fiber amplifier 2, and the other end can be connected to the electric absorption zone to eliminate unnecessary feedback.

[0130] The above is an explanation of the embodiments of the present invention. However, the present invention is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A frequency modulated continuous laser light source, characterized in that: According to the light output direction, the device includes a tunable narrow line width laser, a first semiconductor optical amplifier, a modulator, a wavelength selective reflector and an optical phased array in sequence; An optical isolator and a coupling waveguide are provided between the tunable narrow linewidth laser and the first semiconductor optical amplifier; an optical isolator and a coupling waveguide are provided between the first semiconductor optical amplifier and the modulator; The wavelength selective reflector comprises an incident waveguide and an exit waveguide arranged opposite to each other, at least one microcavity is arranged between the incident waveguide and the exit waveguide, one end of the incident waveguide is connected to the modulator, and the other end is connected to the electric absorption region; The optical phased array includes a waveguide array, a coupling waveguide, a beam splitter and an electrode. The coupling waveguide is used to couple light into the beam splitter. The beam splitter is connected to the coupling waveguide to form a branch signal. The waveguide array receives the branch signal. The electrode is coated on the waveguide array to form a phase tuning area. The phase tuning area realizes the change of the radiation direction of the optical signal under the control of the phase tuning control circuit.

2. The frequency modulated continuous laser light source according to claim 1, characterized in that: An optical isolator and a coupling waveguide are arranged between the modulator and the wavelength selective reflector; an optical isolator and a coupling waveguide are arranged between the wavelength selective reflector and the OPA; and a second SOA is arranged between the wavelength selective reflector and the OPA.

3. The frequency modulated continuous laser light source according to claim 1, characterized in that: The tunable narrow linewidth laser comprises a first epitaxial structure, a first ridge waveguide is grown on the first epitaxial structure, and the first ridge waveguide has a width of 1-4 μm and a height of 1-2 μm.

4. The frequency modulated continuous laser light source according to claim 3, characterized in that: The first epitaxial structure includes a substrate, a buffer layer, a lower confinement layer, a lower waveguide layer, an active layer, an upper waveguide layer, an upper confinement layer, and a contact layer which are arranged in sequence from bottom to top.

5. The frequency modulated continuous laser light source according to claim 4, characterized in that: The active layer includes several layers of In x Ga 1-x As y P 1-y Quantum well, the value range of x is 0-1, the value range of y is 0-1; the number of layers of the quantum well is ≥3 layers.

6. The frequency modulated continuous laser light source according to claim 5, characterized in that: There is a potential barrier between adjacent quantum wells, and the potential barrier is In 0.738 Ga 0.262 As 0.568 P 0.432 .

7. The frequency modulated continuous laser light source according to claim 4, characterized in that: The buffer layer is N + -InP, thickness is 0.5~1μm.

8. The frequency modulated continuous laser light source according to claim 4, characterized in that: The lower limiting layer is N + -InP, thickness is 1~2μm.

9. The frequency modulated continuous laser light source according to claim 4, characterized in that: The lower waveguide layer is InGaAsP with a thickness of 0.1-0.2 μm.

10. The frequency modulated continuous laser light source according to claim 4, characterized in that: The upper waveguide layer is InGaAsP with a thickness of 0.1-0.2 μm.

11. The frequency modulated continuous laser light source according to claim 4, characterized in that: The upper limiting layer is N-InP with a thickness of 1-2.5 μm.

12. The frequency modulated continuous laser light source according to claim 4, characterized in that: The contact layer is P + -InGaAs, thickness is 0.1-0.4μm.

13. The frequency modulated continuous laser light source according to any one of claims 1 to 12, characterized in that: The tunable narrow linewidth laser comprises adjacent laser gain regions and phase shift regions. If the laser gain region is the final light-emitting region, at least one DBR is arranged on the light-emitting side of the laser gain region.

14. The frequency modulated continuous laser light source according to claim 13, characterized in that: If the phase shift region is the final light emitting region, at least one DBR is disposed on the light emitting side of the phase shift region.

15. The frequency modulated continuous laser light source according to claim 13, characterized in that: At least one DBR may be disposed between the laser gain region and the phase shift region.

16. The frequency modulated continuous laser light source according to claim 13, characterized in that: The phase shift region and the laser gain region are arranged on the contact layer of the first epitaxial structure, and electrodes are plated at the contact points for injecting current. The phase shift region and the laser gain region are electrically isolated from each other.

17. The frequency modulated continuous laser light source according to claim 13, characterized in that: The DBR is arranged on the top of the first epitaxial layer structure, and grating grooves are formed between adjacent DBRs, and the depth of the grating grooves is 1-3 μm.

18. The frequency modulated continuous laser light source according to claim 17, characterized in that: The bottom of the grating groove is located at the upper waveguide layer or the upper limiting layer of the first epitaxial structure; an electrical insulating layer and a metal electrode are arranged on the grating groove.

19. The frequency modulated continuous laser light source according to any one of claims 1 to 12, characterized in that: The modulator is any one of an intensity modulator, an electroabsorption modulator or a lithium niobate modulator or a combination of several thereof; the electroabsorption modulator comprises a third epitaxial structure and a ridge waveguide structure, and the ridge waveguide structure is grown on the third epitaxial structure.

20. The frequency modulated continuous laser light source according to claim 19, characterized in that: An electrode is plated on the contact layer of the third epitaxial structure for injecting a modulation current, and the ridge waveguide structure is a deeply etched waveguide structure.

21. The frequency modulated continuous laser light source according to any one of claims 1 to 12, characterized in that: The waveguide array includes a plurality of waveguides, and the waveguides are made of silicon, silicon oxide, silicon nitride, GaAs, InP, InGaAs or InGaAsP.

22. The frequency modulated continuous laser light source according to claim 21, characterized in that: When the waveguide is a silicon-based waveguide, the core width of the waveguide in the waveguide array is a=0.2~0.6μm, the height is h=0.15~0.35μm, the length is L=50~100μm, the period d of the waveguide array is 0.6~1.5μm, and the number of waveguides in the waveguide array is greater than 5.

23. The frequency modulated continuous laser light source according to claim 21, characterized in that: When the waveguide is a GaAs waveguide, the width of the waveguide core layer in the waveguide array is a=1.5~4μm, the height is h=0.8~1.8μm, the length is L=50~100μm, and the number of waveguides in the waveguide array is greater than 5.

24. The frequency modulated continuous laser light source according to any one of claims 1 to 12, characterized in that: At least two microcavities are arranged between the incident waveguide and the exit waveguide, and the microcavities are in the shape of a ring, a disk, a sphere or a square.

25. The frequency modulated continuous laser light source according to any one of claims 1 to 12, characterized in that: The incident end of the output waveguide is connected to the electric absorption region, and the output end is connected to the optical array OPA or the second SOA.

26. The frequency modulated continuous laser light source according to any one of claims 1 to 12, characterized in that: The length of the output waveguide and the input waveguide is 100-200 μm, the height is 0.5-3 μm, and the width is 1-6 μm.

27. The frequency modulated continuous laser light source according to any one of claims 1 to 12, characterized in that: There is a certain gap between the incident waveguide, the output waveguide and the microcavity, and the width of the gap is 0.5-10 μm.

28. The frequency modulated continuous laser light source according to any one of claims 1 to 12, characterized in that: The wavelength selective reflector is made of silicon, silicon oxide, silicon nitride, InP, InGaAsP, GaAs, InGaAs or organic semiconductor.

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