Compact monolithic dual-wavelength distributed feedback laser device and manufacturing method thereof

Abstract

The invention discloses a compact monolithic dual-wavelength distributed feedback laser device and a manufacturing method thereof, and belongs to the technical field of laser, the laser device is composed of a front part, a middle part and a rear part, and the middle part comprises two equivalent Pi phase shift chirp sampling gratings. The laser is based on a reconstruction equivalent chirp technology and has a tunable wavelength interval. A chirp sampling grating with two equivalent phase shifts is arranged in the laser, and the grating is composed of a front part, a middle part and a rear part. Phase matching is achieved through the microstructure quasi-phase matching technology, it is ensured that a laser resonant cavity reaches the phase matching condition at the phase shift position, and wide-range adjustment expanded from 59.50 GHz to 116.25 GHz can be effectively achieved by changing injection current. The invention has the advantages of accurate wavelength control, simple structure, low power consumption, high integration level and the like.

Description

Technical Field

[0001] The invention belongs to the field of laser technology and relates to a laser, in particular to a compact single-chip dual-wavelength distributed feedback laser device and a manufacturing method thereof. Background Art

[0002] Dual-wavelength distributed feedback (DFB) lasers have been widely studied as key optical sources in fields such as optical sensing, millimeter wave generation, lidar, and terahertz communication. Conventional dual-wavelength sources consisting of two separately packaged lasers can partially meet these requirements, but have disadvantages such as low reliability, high power consumption, and large footprint. With the progress of semiconductor technology and integrated photonics, monolithic integrated dual-wavelength lasers can effectively solve these problems. Among them, distributed feedback and distributed Bragg reflector (DBR) lasers are the most common light sources with advantages such as single longitudinal mode, low threshold, and stable lasing wavelength. However, the fabrication of the Bragg gratings required for both relies on electron beam lithography, which has problems such as splicing errors and proximity effects. Recently, in order to simplify the manufacturing process and improve the accuracy of the laser wavelength, the REC technology, that is, the design of sampled gratings, has been proposed. Due to these advantages, the monolithic integration solution has become the mainstream direction and provides an alternative for applications in fields such as communications, sensing, and microwave photonics.

[0003] Dual-wavelength lasers use optical heterodyning to generate microwaves. The bottlenecks of discrete solutions in terms of size, weight, and power can be solved by photonic integration. Microwave signals can be generated by connecting two DFB lasers in series. However, this method requires additional supplementary means, such as optical sideband injection modulated by radio signals, phase splitting, etc., which greatly increases the manufacturing complexity and cost of dual-wavelength lasers. Dual-mode lasers can stably emit two laser modes at the same time, but the fixed frequency interval and poor tunable range limit their applications. Therefore, there is currently a lack of a monolithic highly integrated tunable dual-wavelength light source solution. Summary of the invention

[0004] In view of the problems in the prior art, the present invention provides a compact monolithic dual-wavelength distributed feedback laser device and a manufacturing method thereof, which can achieve precise wavelength control, has a simple structure, low power consumption and high integration.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a compact monolithic dual-wavelength distributed feedback laser device, wherein the laser consists of three parts: front, middle and rear parts, wherein the middle part contains two equivalent π-phase-shifted chirped sampling gratings.

[0007] Furthermore, the laser is injected with current from the front, middle and rear parts respectively; the laser wavelength interval changes with the change of the injection current of the front and rear parts. Specifically, the Bragg wavelength interval of the laser is precisely controlled by reconstructing the equivalent chirp technology, and by changing the injection current of the laser, the carrier concentration and temperature are affected, and then the effective refractive index of the injection area is changed, thereby achieving a wavelength interval tuning range of up to tens of GHz.

[0008] Furthermore, the seed grating and sampling structure of the chirped sampled grating are a uniform Bragg grating and a linear chirped sampling structure respectively, and the chirped sampled grating is evenly divided into three parts.

[0009] Furthermore, the reconstruction equivalent chirp (REC) technology is used to control the periodic variation of the sampling structure and thus equivalently realize the function of the chirped Bragg grating, and the two equivalent π phase shifts are introduced into the intervals between the three parts of the chirped sampled grating to achieve precise control of the wavelength interval.

[0010] In principle, the present invention suppresses grating interference based on a linear dispersion grating and a double π phase shift to ensure dual-mode stable lasing. The dispersion grating acts as a resonant cavity, and the period at its phase shift position determines the laser wavelengths of the two modes. In addition, the introduction of a multi-electrode scheme makes current injection more flexible, thereby achieving tunability of the wavelength interval. Specifically, by designing a chirped sampled grating, two laser modes of different wavelengths are achieved. The chirped sampled grating has a periodically changing refractive index, which allows two light waves of different wavelengths to form standing waves in the grating, thereby generating two different lasing wavelengths. Introducing two equal π phase shifts in the chirped sampled grating helps to form two independent resonant cavities in different parts of the grating, each corresponding to a lasing wavelength. This structure helps to stabilize dual-wavelength lasing and reduce competition between modes. The two π phase shifts form two wavelengths in the middle part, long wave and short wave. The current injected into the front part affects the long wave mode, and the current injected into the rear part affects the short wave mode. That is, by changing the injected current of the front and rear parts, the effective refractive index of the corresponding parts can be changed, thereby adjusting the mode interval of the dual-wavelength laser.

[0011] By changing the current injected into the front, middle and rear parts of the laser, the effective refractive index of the corresponding part can be adjusted, thereby achieving precise tuning of the wavelength interval. Using the transfer matrix method, the relationship between the mode spacing and the Bragg spacing of the dual-wavelength laser with different refractive index modulation amplitudes Δn0 is studied. For the sampled grating, the refractive index modulation change can be derived as:

[0012]

[0013] Where Δn(z) is the refractive index modulation change, z is used to represent any complex number, j is the imaginary number symbol, Λ0 and Δn0 are the period and refractive index modulation amplitude of the seed grating, respectively, and F m is the m-order Fourier coefficient, P is the sampling structure period, ΔP is the sampling grating period difference, and cc represents a constant.

[0014] By changing the injection current, the laser can achieve a tuning range from 59.50 GHz to 116.25 GHz in the C band. When the injection current exceeds a certain value, the competition between modes intensifies, causing one mode to disappear and the laser to operate in a single-mode state.

[0015] Furthermore, the laser is composed of a substrate layer, a buffer layer, a lower confinement layer, a multi-quantum well layer, an upper confinement layer, a grating layer, a buried layer, a corrosion barrier layer, a waveguide layer and a contact layer stacked from bottom to top.

[0016] Furthermore, the laser epitaxial material is grown in multiple layers using metal organic chemical vapor deposition (MOCVD) technology.

[0017] Furthermore, the multi-quantum well layer is an InGaAlAs structure and is a gain medium of the laser; the grating layer is a p-type InGaAsP grating layer, and the operating wavelength of the p-type InGaAsP grating layer is located at the center of the gain bandwidth.

[0018] Furthermore, the substrate layer is an n-type doped material; the lower confinement layer is composed of n-type doped and non-doped materials to form a confinement effect.

[0019] Furthermore, the laser is a ridge waveguide structure.

[0020] In a second aspect, the present invention also provides a method for manufacturing the above-mentioned compact monolithic dual-wavelength distributed feedback laser device: sequentially growing a buffer layer and a lower confinement layer on a substrate by metal organic compound vapor deposition; growing a multi-quantum well layer on the lower confinement layer; growing an upper confinement layer on the multi-quantum well layer; depositing a grating above the upper confinement layer as a grating layer; utilizing holographic exposure technology in combination with photolithography and etching processes to prepare a chirped sampling grating; growing a buried layer above the grating layer, and sequentially growing a corrosion barrier layer, a waveguide layer and a contact layer on the buried layer; corroding the waveguide layer and the contact layer to form a ridge shape, and obtaining mutually isolated front, middle and rear parts by etching.

[0021] In terms of manufacturing process, the present invention adopts REC technology, and the manufacturing of seed grating and sampling structure is divided into two steps: first, holographic exposure of seed grating, and then micron-level contact exposure of sampling structure. Through the carefully designed epitaxial wafer, the Bragg wavelength is kept away from the center of the gain region, ensuring lasing. The present invention realizes fine nanostructures, including dispersion grating and phase shift, through REC technology, which significantly reduces manufacturing cost and complexity.

[0022] The beneficial effects of the present invention are as follows: the present invention provides a compact monolithic dual-wavelength distributed feedback laser device and a method for manufacturing the same, which uses REC technology to simplify the manufacturing process and reduce costs; through a three-stage structural design, precise tuning of the wavelength interval is achieved. Specifically, the laser uses a chirped sampling grating and two equivalent π phase shifts to achieve dual-wavelength lasing, and controls the wavelength interval by adjusting the injected current, thereby significantly expanding the tuning range of the wavelength interval while reducing the size of the laser. This design not only simplifies the structure of the laser, but also reduces the manufacturing cost and improves the performance of the laser. The laser device of the present invention has the advantages of compact structure, wide tuning range, stable performance, etc., and has application potential in the fields of optical communications and optical sensing. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 is a schematic diagram of a compact monolithic dual-wavelength distributed feedback laser device of the present invention;

[0024] Figure 2 It is a microscopic top view of the compact monolithic dual-wavelength distributed feedback laser device of the present invention;

[0025] Figure 3 It is the PI curve of the compact monolithic dual-wavelength distributed feedback laser device of the present invention in the current range of 0 to 240 mA;

[0026] Figure 4 The compact monolithic dual-wavelength distributed feedback laser device of the present invention is used in semiconductor optical amplifier current I SOA Mapping of the C-band spectrum and the wavelength shift of the two modes in the case of high Δn0 (Δn0 = 0.0016) in the range of 0 to 60 mA;

[0027] Figure 5 is the current I injected into the rear section of the compact monolithic dual-wavelength distributed feedback laser device of the present invention front Mapping of the O-band spectrum and the wavelength shifts of the two modes in the case of low Δn0 (Δn0=0.0005) in the range of 90~120mA. DETAILED DESCRIPTION

[0028] The specific implementation of the present invention is described below with reference to the accompanying drawings.

[0029] like Figure 1 and Figure 2 As shown, the present invention provides a compact monolithic dual-wavelength distributed feedback laser device. The laser device includes a laser resonant cavity composed of three parts: front, middle and back, wherein the middle part has two equivalent π-phase-shifted chirped sampling gratings. The grating has a phase shift structure, and the phase shift structure is used to achieve phase matching of the laser resonant cavity through microstructure quasi-phase matching technology.

[0030] The semiconductor laser is composed of a substrate layer, a buffer layer, a lower confinement layer, a multi-quantum well layer, an upper confinement layer, a grating layer, a buried layer, a corrosion barrier layer, a waveguide layer and a contact layer stacked from bottom to top.

[0031] The method for manufacturing a semiconductor laser is as follows: first, an n-type doped substrate is used, and then the following layers are grown on the substrate in sequence by metal organic compound vapor deposition technology: an n-type doped InP buffer layer, an n-type doped lower confinement layer, and a p-type doped lower confinement layer. The lower confinement layer is used to confine the light field and bind carriers. After the growth of these layers is completed, the InGaAlAs multi-quantum well layer is then grown. An upper confinement layer is designed above the multi-quantum well layer, an InGaAsP grating layer is grown above the upper confinement layer, a p-type InP layer is grown above the grating layer for burial (i.e., a buried layer), and an etching barrier layer, a waveguide layer, and a contact layer are grown in sequence on the buried layer. The waveguide layer and the contact layer are etched to form a ridge shape, and the front, middle, and rear parts that are isolated from each other are obtained by etching. Among them, the chirped sampling grating is manufactured by holographic exposure technology, combined with conventional photolithography and subsequent etching processes.

[0032] The grating is made by using microstructure quasi-phase matching technology and REC technology to reduce the threshold of the laser and optimize the wavelength selection characteristics, and to increase the group delay of the grating structure to reduce the threshold current.

[0033] The production of seed gratings relies on holographic exposure technology. In this process, a laser light source needs to be properly modulated to form the desired grating pattern. Holographic exposure technology projects an interference beam onto a photosensitive material to form phase and amplitude modulation, thereby writing the periodic structure of the seed grating. In this process, the period and depth of the grating need to be very precise to ensure the subsequent optical performance, such as precise control of the Bragg wavelength.

[0034] The production of sampling structures relies on micron-scale contact exposure technology. In this process, micron-scale photolithography technology is used to transfer the predetermined pattern to the photosensitive material through contact exposure. Contact exposure can achieve higher-precision structural etching and is suitable for the production of microstructures. The design of the sampling structure involves the optimization of the light transmission characteristics and local enhancement effects to ensure the stable output of the laser.

[0035] In order to ensure the smooth progress of the lasing process, the design of the seed grating and sampling structure also needs to consider the distribution characteristics of the Bragg wavelength, and the epitaxial wafer needs to be designed reasonably. When designing the epitaxial wafer, it is necessary to ensure that the Bragg wavelength is far away from the center of the gain region where the Bragg wavelength of the first-order sub-grating is located. The purpose of this design is to adjust the material parameters of the epitaxial wafer so that the laser output in the gain region can effectively avoid the peak position of the Bragg wavelength, thereby avoiding gain saturation or energy loss and ensuring stable lasing of the laser.

[0036] In a specific embodiment, the output spectrum of the laser under different injection current conditions is recorded, and the change in wavelength spacing is measured using a spectrum analyzer. Experimental results show that by adjusting the injection current, the wavelength spacing of the dual-wavelength laser can be accurately controlled, and a tuning range from 59.50 to 116.25 GHz is achieved. Specifically, the total length of the prepared DFB laser chip is 1000 μm, the total width is 250 μm, the front and rear sections are both coated with an anti-reflection film with a reflectivity of 0.5%, and the lengths of the front, middle, and rear sections are 225 μm, respectively. The spectrum analyzer is used to record the output spectrum of the laser. The seed grating depth of the DFB laser is 60 nm, and the refractive index modulation amplitude Δn0 is 0.0016. In order to estimate the tuning range of the laser, the frequency spacing is used instead of the wavelength spacing for measurement. Figure 3 The current-power (PI) characteristics of a DFB laser operating in the 1550nm band are shown. SOA Under the conditions of 40mA and 25℃ respectively, the threshold current of the laser is 32.4mA and the maximum output power is 24.33mW.

[0037] Regarding the impact of different chirp rates and phase shift structures on laser performance: Experimental results show that a lower chirp rate helps achieve a narrower wavelength spacing, but it also increases the laser cavity length, which may affect the integration and power consumption of the laser. Therefore, in the design process, it is necessary to comprehensively consider the trade-off between chirp rate and cavity length to achieve optimal performance.

[0038] By adjusting the injection current of each segment, the wavelength tuning range of the C-band laser can be observed under high Δn0 conditions. SOA When the range is 0~60mA, the spectrum of C-band laser and the displacement mapping relationship between the two mode wavelengths are as follows: Figure 4 By recording the local maximum, the peak wavelengths of the two modes (λ1 and λ2) can be depicted, and their difference is an important performance parameter of the wavelength tunable DFB laser.

[0039] By adjusting I SOA ,I front and I rear, the total tuning range of the DFB laser under low Δn0 is 18.85~38.31GHz. Selecting low Δn0 can achieve a narrower wavelength interval (about 20GHz), a feature that is often overlooked in existing DFB laser research. Figure 5 As shown, the current cross-sectional current I front When the current exceeds 115 mA, the laser undergoes mode hopping due to mode competition. In addition, lower Δn0 and longer cavity length may lead to the deterioration of the side mode suppression effect. Due to the resolution limitation of the spectrum analyzer and the high requirements for narrow wavelength interval measurement, the measured laser wavelength curve fluctuates less than the C-band result.

[0040] In summary, the present invention achieves precise control of wavelength interval and wide-range tuning through innovative structural design and manufacturing process, and has broad application prospects. At the same time, the present invention also provides a direction for further optimization of laser performance, which is expected to significantly improve its performance and application value.

[0041] In the present invention, unless otherwise specified, the scientific and technical terms used herein have the meanings commonly understood by those skilled in the art. In addition, the reagents, materials and operating procedures used herein are reagents, materials and conventional procedures widely used in the corresponding fields.

[0042] It should be noted that the terms such as "upper", "lower", "left", "right", "front", "back", etc. cited in the invention are only for the convenience of description and are not used to limit the scope of implementation of the present invention. Changes or adjustments in their relative relationships should be regarded as the scope of implementation of the present invention without substantially changing the technical content.

[0043] Finally, it should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein by equivalents. 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 compact monolithic dual-wavelength distributed feedback laser device, characterized in that: The laser consists of three parts: front, middle and rear parts, wherein the middle part contains two equivalent π-phase-shifted chirped sampling gratings.

2. The compact monolithic dual-wavelength distributed feedback laser device according to claim 1, characterized in that: The laser is injected with currents from the front, middle and rear parts respectively; the wavelength interval of the laser changes with the change of the currents injected from the front and rear parts.

3. The compact monolithic dual-wavelength distributed feedback laser device according to claim 1, characterized in that: The seed grating and sampling structure of the chirped sampling grating are respectively a uniform Bragg grating and a linear chirped sampling structure, and the chirped sampling grating is evenly divided into three parts.

4. The compact monolithic dual-wavelength distributed feedback laser device according to claim 3, characterized in that: The two equivalent π phase shifts are introduced in the intervals of the three parts of the chirped sampled grating.

5. The compact monolithic dual-wavelength distributed feedback laser device according to claim 1, characterized in that: The laser is composed of a substrate layer, a buffer layer, a lower confinement layer, a multi-quantum well layer, an upper confinement layer, a grating layer, a buried layer, a corrosion barrier layer, a waveguide layer and a contact layer stacked in sequence from bottom to top.

6. The compact monolithic dual-wavelength distributed feedback laser device according to claim 5, characterized in that: The laser epitaxial material is grown in multiple layers by adopting metal organic chemical vapor deposition technology.

7. The compact monolithic dual-wavelength distributed feedback laser device according to claim 5, characterized in that: The multi-quantum well layer is an InGaAlAs structure and is a gain medium of the laser; the grating layer is a p-type InGaAsP grating layer, and the operating wavelength of the p-type InGaAsP grating layer is located at the center of the gain bandwidth.

8. The compact monolithic dual-wavelength distributed feedback laser device according to claim 5, characterized in that: The substrate layer is an n-type doped material; The lower confinement layer is composed of n-type doped and non-doped materials to form a confinement effect.

9. The compact monolithic dual-wavelength distributed feedback laser device according to claim 1, characterized in that: The laser is a ridge waveguide structure.

10. The method for manufacturing a compact monolithic dual-wavelength distributed feedback laser device according to any one of claims 1 to 9, characterized in that: A buffer layer and a lower confinement layer are sequentially grown on a substrate by metal organic compound vapor deposition; a multi-quantum well layer is grown on the lower confinement layer; an upper confinement layer is grown on the multi-quantum well layer; a grating is deposited on the upper confinement layer as a grating layer; a chirped sampling grating is prepared by using holographic exposure technology combined with photolithography and etching processes; a buried layer is grown on the grating layer, and a corrosion barrier layer, a waveguide layer and a contact layer are sequentially grown on the buried layer; The waveguide layer and the contact layer are corroded to form a ridge shape, and three mutually isolated front, middle and rear parts are obtained by etching.

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