A monolithic integrated square-FP coupled cavity laser array and its preparation method

Abstract

The present disclosure provides a monolithic integrated square-FP coupled cavity laser array, comprising: a laser array, wherein each laser includes a square whispering gallery microcavity angularly connected to the first end of an FP cavity, the size of each square whispering gallery microcavity is different, and the size of each FP cavity is the same; a multimode interference coupler for combining the lasers of the laser array and outputting them; a curved waveguide, one end of which is respectively connected to the second end of the FP cavity, and the other end of which is connected to the multimode interference coupler. The present disclosure also provides a method for preparing a monolithic integrated square-FP coupled cavity laser array. The semiconductor laser disclosed in the present disclosure has a large wavelength tuning range and a simple preparation process, does not require precise photolithography and secondary epitaxial technology, and has a high production yield and low cost, and has important applications in optical communications.

Description

Technical Field

[0001] The present disclosure relates to the field of semiconductor optoelectronic technology, and in particular to a monolithic integrated square-Fabry-Perot (FP) coupled cavity laser array and a preparation method thereof. Background Art

[0002] In fiber-optic data communication systems, the rapidly growing information capacity requires increasingly higher bit rates for local area network transmission. To meet the growing demand for high-bandwidth and high-speed optical communications, the Institute of Electrical and Electronics Engineers (IEEE) announced the 40G and 100G Ethernet data communication standards in 2010. On the transmitter side, electro-absorption modulated lasers (EMLs) and directly modulated lasers (DMLs) have been developed. Compared to EMLs, DMLs offer advantages such as smaller size, lower cost, lower power consumption, and simpler manufacturing processes, making them suitable for low-cost transmitters. High-speed directly modulated distributed feedback (DFB) lasers, due to their small size, low cost, and low power consumption, are ideally suited as the transmitting light source for short- and medium-distance transmission. Therefore, a four-channel, high-speed, directly modulated DFB laser array with a lasing wavelength of 1.31μm has become the standard transmitter of choice. A 4×25 Gbit / s high-speed directly modulated distributed feedback (DFB) laser array was developed by using a butt-regeneration structure for transitioning between active and passive components and combining the wavelengths using a multimode interference (MMI) coupler. A 4×28 Gbit / s high-speed directly modulated laser array was achieved using active distributed reflector DFB (ADR-DFB) lasers. A four-channel DFB laser array was fabricated using an optimized selective area growth method, enabling 40 Gb / s data transmission. However, these technologies are complex to manufacture, and simpler fabrication steps are needed. Summary of the Invention

[0003] (1) Technical issues to be solved

[0004] To address the above problems, the present disclosure provides a monolithic integrated square-FP coupled cavity laser array and a preparation method, which are used to at least partially solve the technical problems of traditional semiconductor lasers such as difficulty in achieving wide-range wavelength tuning and complex preparation processes.

[0005] (2) Technical solution

[0006] On the one hand, the present disclosure provides a monolithic integrated square-FP coupled cavity laser array, comprising: a laser array, wherein each laser includes a square whispering gallery microcavity angularly connected to the first end of an FP cavity, each square whispering gallery microcavity has different dimensions, and each FP cavity has the same dimensions; a multimode interference coupler for combining lasers from the laser array and outputting the combined lasers; and a curved waveguide, one end of which is connected to the second end of the FP cavity and the other end of which is connected to the multimode interference coupler.

[0007] Furthermore, the side lengths of the square whispering gallery microcavity form an arithmetic progression.

[0008] Furthermore, the interval g between each FP cavity is 250 μm.

[0009] Furthermore, the depth h of the square whispering gallery microcavity and the FP cavity ranges from 4 to 5 μm.

[0010] Furthermore, the laser array includes four channels, eight channels, and sixteen channels.

[0011] Furthermore, the square whispering gallery microcavity includes an electric triggering structure.

[0012] Furthermore, the substrates of the square whispering gallery microcavity and the FP cavity include materials composed of group III and group V elements.

[0013] Furthermore, the active layers of the square whispering gallery microcavity and the FP cavity include one of quantum wells, quantum wires and quantum dots.

[0014] Furthermore, a gap is provided at the connection between the curved waveguide and the FP cavity. The length of the gap is 1 to 1.5 μm, and the width of the gap is the same as the width of the FP cavity.

[0015] Another aspect of the present disclosure provides a method for preparing a monolithic integrated square-FP coupled cavity laser array, comprising: S1, photolithographically etching a cavity on an epitaxial wafer, the cavity comprising a laser array, a multimode interference coupler, and a curved waveguide, wherein each laser in the laser array comprises a square whispering gallery microcavity angularly connected to the first end of an FP cavity, the dimensions of each square whispering gallery microcavity being different, and the dimensions of each FP cavity being the same; the multimode interference coupler being used to combine the lasers of the laser array and output them; one end of the curved waveguide being connected to the second end of the FP cavity, and the other end being connected to the multimode interference coupler; S2, continuing ICP etching of the cavity; S3, filling and etching BCB; S4, etching an isolation groove between the square whispering gallery microcavity and the FP cavity; and S5, evaporating electrodes to obtain a monolithic integrated square-FP coupled cavity laser array.

[0016] (3) Beneficial effects

[0017] The monolithic integrated square-FP coupled cavity laser array provided by this disclosure combines a square whispering gallery microcavity with an FP cavity to form strong mode coupling. Furthermore, by controlling the size of the square whispering gallery microcavity to change the optical path of the fundamental mode, the lasing wavelength is shifted at equal intervals, thereby achieving equal wavelength tuning of the entire laser array. This semiconductor laser has a wide wavelength tuning range, a simple manufacturing process with few steps, and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematically shows a structural diagram of a monolithically integrated square-FP coupled cavity laser array according to an embodiment of the present disclosure;

[0019] Figure 2 Schematically shows a microscope image of a monolithically integrated square-FP coupled cavity laser array according to an embodiment of the present disclosure;

[0020] Figure 3 (a) schematically illustrates a curved waveguide according to an embodiment of the present disclosure;

[0021] Figure 3 (b) schematically illustrates a graph showing the relationship between the loss and the bending radius of a curved waveguide according to an embodiment of the present disclosure;

[0022] Figure 4 (a) schematically shows a schematic diagram of a multimode interference coupler according to an embodiment of the present disclosure;

[0023] Figure 4 (b) schematically shows a mode field distribution diagram of light along the waveguide transmission direction obtained by simulating a multimode interference coupler according to an embodiment of the present disclosure;

[0024] Figure 5 Schematically shows a graph of the power of the output light of each channel coupled to the single-mode optical fiber and the FP cavity current of 0 to 100 mA according to an embodiment of the present disclosure;

[0025] Figure 6 Schematically shows a spectrum diagram according to an embodiment of the present disclosure;

[0026] Figure 7 The diagram schematically shows a large signal eye diagram at 25 Gb / s according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0027] In order to make the objectives, technical solutions and advantages of the present disclosure more clearly understood, the present disclosure is further described in detail below in conjunction with specific embodiments and with reference to the accompanying drawings.

[0028] In the present disclosure, unless otherwise specified, "having a component" is not limited to having a single component, but may include one or more components. Furthermore, the use of ordinal numbers such as "first" and "second" in the specification and claims to modify components in the claims does not itself imply or represent any previous ordinal number of the component, nor does it represent the order of one component to another or the order in the manufacturing method. The use of such ordinal numbers is only used to clearly distinguish a component with a certain name from another component with the same name.

[0029] In this disclosure, words such as "include," "contain," and "have" are open-ended words and should be interpreted as meaning "including but not limited to..." Therefore, when the terms "include," "contain," and / or "have" are used in the description of this disclosure, they specify the presence of corresponding features, regions, steps, operations, and / or components, but do not exclude the presence of one or more corresponding features, regions, steps, operations, and / or components.

[0030] In the present disclosure, the terms “a range from a first value to a second value” and “a range between a first value and a second value” mean that the range includes the first value, the second value and other values ​​therebetween.

[0031] The embodiments of the present disclosure provide a monolithically integrated square-FP coupled cavity laser array, see Figure 1 , including: a laser array 110, wherein each laser includes a square whispering gallery microcavity 111 / 112 / 113 / 114 angularly connected to the first end of a FP cavity 115, each square whispering gallery microcavity has a different size, and each FP cavity has the same size; a multimode interference coupler 130 for combining the lasers of the laser array and outputting them; and curved waveguides 121 / 122 / 123 / 124, each having one end connected to the second end of the FP cavity and the other end connected to the multimode interference coupler 130.

[0032] Whispering gallery mode microcavity (WGM) uses the total reflection of light at the interface to form a resonant mode. It has the advantages of small size, low threshold, low power consumption, and easy integration, and is widely used in photonic integrated circuits, optical interconnection, optical communications, and microwave photonics. Compared with traditional semiconductor lasers, square whispering gallery microcavity lasers have shown obvious advantages in direct high-speed modulation due to their high quality factor and small size. The combination of square whispering gallery microcavity and FP cavity can achieve characteristics such as high speed, high power and directional output. The square-FP coupled cavity laser with a lasing wavelength of 1.55μm has a side mode suppression ratio (SMSR) greater than 40dB and a 3-dB modulation response bandwidth of 15.5GHz.

[0033] The present disclosure further achieves the purpose of evenly spaced shift of the lasing wavelength by controlling the size differences between the square whispering gallery microcavities 111 / 112 / 113 / 114 in the laser array, thereby changing the optical path of the fundamental mode in the square whispering gallery microcavities, thereby realizing evenly spaced wavelength tuning of the entire laser array.

[0034] Laser array 110 emits laser beams. Curved waveguides 121 / 122 / 123 / 124, also known as S-shaped waveguides, transmit the laser beams to a multimode interference coupler (MMI) with minimal loss. Multimode interference coupler 130 combines four laser beams of different wavelengths for output from a single waveguide. The disclosed semiconductor laser operates by emitting laser light from a multi-channel square whispering gallery-FP coupled cavity laser, which is then transmitted via curved waveguides to the MMI for combined output.

[0035] Compared to conventional DFB laser arrays, the semiconductor laser disclosed in this paper offers a wider wavelength tuning range, a simpler manufacturing process, fewer process steps, and lower costs. Furthermore, the entire manufacturing process does not require the combination of active and passive technologies, reducing the number of process steps. Losses caused by the curved waveguide and multimode interference coupler are compensated using electrical current.

[0036] Based on the above embodiment, the side lengths of the square whispering gallery microcavity form an arithmetic progression.

[0037] Due to the limitations of photolithography precision and process errors in the actual process, the lasing wavelength spacing of each laser is mainly controlled by the size of the table. On the other hand, the current injected into the square microcavity and the FP cavity can be finely adjusted to the required wavelength. The larger the required wavelength spacing, the greater the difference between the side lengths of the squares. For example, when the channel spacing is 5nm, the side length difference of the squares is generally set to 0.1μm, and when the channel spacing is 3nm, the side length difference is set to about 0.07μm.

[0038] Based on the above embodiment, the interval g between each FP cavity is in the range of 250 μm.

[0039] The spacing between each channel of the laser is mainly to take into account the influence of thermal crosstalk during actual operation. The spacing of 250μm can ensure that all channels are affected as little as possible by other channels when they are working normally.

[0040] Based on the above embodiment, the depth h of the square whispering gallery microcavity and the FP cavity ranges from 4 to 5 μm.

[0041] The reason for this depth is to reduce the loss in the vertical direction, to ensure that the light leaking upward from the active area is reflected by the upper surface and then interferes with the light leaking downward. The etching depth reaches more than 4μm to further reduce the loss of the cavity.

[0042] Based on the above embodiments, the laser array includes four channels, eight channels, and sixteen channels.

[0043] For example, Figure 1 The example shows a four-channel laser array, but this is not limited to four channels. Eight-channel and sixteen-channel laser arrays can be used in 400GE scenarios. Laser arrays with different channels only require different curved waveguide and multimode interference coupler dimensions.

[0044] Based on the above embodiment, the square whispering gallery microcavity includes an electric triggering structure.

[0045] The top layer of the square whispering gallery microcavity is provided with a P electrode, such as Figure 2 shown.

[0046] Based on the above embodiment, the substrates of the square whispering gallery microcavity and the FP cavity include materials composed of group III and group V elements.

[0047] The entire monolithically integrated square-FP coupled cavity laser array can be made of gallium arsenide, indium phosphide or other Group III-V materials.

[0048] Based on the above embodiments, the active layer of the square whispering gallery microcavity and the FP cavity can be one of quantum wells, quantum wires and quantum dots.

[0049] The active layer may be any common active layer.

[0050] On the basis of the above embodiment, a gap is provided at the connection between the curved waveguide and the FP cavity. The length of the gap is 1-1.5 μm, and the width of the gap is the same as the width of the FP cavity.

[0051] The gap is to form a reflective end face of the FP to enable lasing.

[0052] The present disclosure also provides a method for preparing a square whispering gallery microcavity-FP coupled cavity semiconductor laser, comprising:

[0053] The square FP coupled cavity laser array, curved waveguide, and MMI are etched onto the epitaxial wafer using photolithography. Three topologies are created. The cavity structure is etched using ICP. The cavity structure includes the square whispering gallery microcavity, the FP microcavity, the groove between the FP cavity's light-emitting end and the curved waveguide, the curved waveguide, and the MMI. It is important to note that the groove connecting the FP cavity's light-emitting surface and the curved waveguide is distinct from the electrical isolation groove between the square whispering gallery microcavity and the FP cavity. This groove serves as a reflective end facet for the FP cavity. To maintain fabrication precision, the groove length is 1-1.5 μm using a standard photolithography machine. Using a higher-precision projection lithography machine, this length can be shortened to minimize optical power loss. The depth is the same as for the square whispering gallery microcavity and FP cavity. The electrical isolation groove is simply created by etching away the ohmic contact layer during fabrication, allowing for separate electrical injection between the square whispering gallery microcavity and the FP cavity. Next, BCB filling and etching are performed, followed by photolithography of the electrode window and patterned electrodes. Finally, thinning, polishing, and cleavage testing are performed.

[0054] The laser disclosed in this paper is manufactured using standard photolithography and inductively coupled plasma etching techniques. The elimination of holographic lithography or epitaxial regrowth techniques significantly simplifies the manufacturing process and reduces costs. Commercial epitaxial wafers are considered for producing HSRLs with a lasing wavelength of 1.31 μm, combined with curved waveguides and MMI for wave combining to achieve an array light source. The wavelength spacing of the laser produced by this method is 5 nm, which meets the standard. Furthermore, the loss of the curved waveguide and the transmission loss of the multimode interference coupler should be designed to be as small as possible.

[0055] The present disclosure is further described below through specific embodiments. A four-channel square-FP coupler laser integrated on a single chip is described in detail below.

[0056] This four-channel square whispering gallery microcavity-FP coupled cavity semiconductor laser array features four square whispering gallery microcavities 111 / 112 / 113 / 114 with varying side lengths, designed to suit wavelength spacing. The structure is a deep-etched whispering gallery microcavity with a depth of 4.2μm. Four identically sized FP cavities 115 are formed. A gap of 1μm in length and 1.6μm in width separates the four ports at the other end of the FP cavity 115 from the curved waveguides 121 / 122 / 123 / 124. This creates a reflective end facet for the FP, enabling lasing.

[0057] The curved waveguides 121 / 122 / 123 / 124 are used to connect the FP cavity of the four-channel laser array and the multi-mode interference coupler 130 respectively.

[0058] The multimode interference coupler 130 is used to combine four wavelengths, and its output port 131 is used for light output.

[0059] The output light of the four lasers of the above-mentioned monolithically integrated four-channel square whispering gallery microcavity-FP coupled cavity semiconductor laser is transmitted to the multimode interference coupler through a curved waveguide, and is then combined by the multimode interference coupler and output from its output end.

[0060] The square whispering gallery microcavities 111 / 112 / 113 / 114 of the monolithically integrated four-channel square whispering gallery microcavity-FP coupled cavity semiconductor laser have side lengths of 10, 10.05, 10.1, and 10.15 μm, respectively. The angularly connected FP cavity 115 has a cavity length L of 300 μm and a width d of 1.6 μm. The substrate material used to fabricate the monolithically integrated four-channel square whispering gallery microcavity-FP coupled cavity laser is indium phosphide, and the active layer is an aluminum gallium steel arsenide multiple quantum well structure.

[0061] The bending radii of the curved waveguides 121 / 122 / 123 / 124 are 900, 1200, 1200 and 900 μm respectively, so that the laser outputs of the four channels are transmitted to the multimode interference coupler 130 with minimal loss.

[0062] like Figure 4 As shown, the length L of the multimode interference coupler (MMI) 130 mmi =72μm, width W mmi =10.4μm, the width of each input terminal d mmi =1.6μm, interval D Gap =1μm.

[0063] like Figure 2 , which is a microscope image of a four-channel square-FP coupler laser fabricated from the monolithically integrated four-channel square whispering gallery microcavity-FP coupler cavity laser proposed in this embodiment. It can be seen that the morphology of the fabricated laser array is intact.

[0064] like Figure 3 As shown in FIG. 1 , (a) a schematic diagram of the S-shaped curved waveguide in the monolithically integrated four-channel square-FP coupled cavity laser proposed in this embodiment and (b) a curve showing the relationship between the waveguide loss and the bending radius obtained by simulation. It can be seen that when the bending radius of the curved waveguide is greater than 850 μm, the bending loss is basically 0. In actual design, the bending radius is generally greater than 850 μm.

[0065] like Figure 4As shown in FIG. 1 , (a) a schematic diagram of the MMI in the monolithically integrated four-channel square-FP coupled cavity laser proposed in this embodiment and (b) the simulated mode field distribution of light along the waveguide transmission direction. It can be seen that light can be transmitted in the fundamental mode when propagating in the MMI.

[0066] like Figure 5 The graph shows the power of the output light coupled into the single-mode fiber for each channel of the square microcavity at a bias current of 15 mA, versus the FP cavity injection current from 0 to 100 mA. It can be seen that the output power of each channel is greater than 6 mW, which is sufficient for practical applications.

[0067] Figure 6 The optical spectra corresponding to the square whispering gallery microcavity injection current ISQ and FP cavity injection current IFP for channels 1, 2, 3 and 4 are I1SQ=10mA, I1FP=46mA, I2SQ=10mA, I2FP=65mA, I3SQ=35mA, I3FP=75mA and I4SQ=38mA, I4FP=78mA, respectively, with a wavelength interval of 5nm, meeting the design requirements.

[0068] Figure 7 The clear eye diagram of 25Gb / s is measured when the square whispering gallery microcavity injection current ISQ and FP cavity injection current IFP of channels 1, 2, 3 and 4 are I1SQ=10mA, I1FP=46mA, I2SQ=10mA, I2FP=65mA, I3SQ=35mA, I3FP=75mA and I4SQ=38mA, I4FP=78mA, respectively, which can meet the data transmission speed of 100Gb / s in practical applications.

[0069] The monolithic integrated four-channel square whispering gallery microcavity-FP coupled cavity array proposed in this disclosure has the following beneficial effects:

[0070] 1. The four-channel laser array has a large wavelength tuning range. By controlling the size of the square whispering gallery microcavity, the wavelength can be guaranteed to have a theoretical wavelength interval. The error caused by the process can be finely tuned by adjusting the injection current of the square and FP cavities to obtain the required wavelength range.

[0071] 2. The four-channel laser array proposed in this disclosure requires deep etching during the etching process, with an etching depth of about 4.2 μm. The etching of the curved waveguide and MMI also needs to ensure that they pass through the active area. In this way, the required pattern can be obtained by etching in one step during the process implementation, reducing the process steps and optimizing the process flow.

[0072] 3. The monolithically integrated four-channel laser array proposed in this disclosure does not require secondary epitaxy and precise photolithography technology, and has the advantages of simple manufacturing process, high yield, and low cost, and has important applications in optical communications.

[0073] The specific embodiments described above further illustrate the purpose, technical solutions and beneficial effects of the present disclosure. It should be understood that the above are only specific embodiments of the present disclosure and are not intended to limit the present disclosure. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present disclosure should be included in the scope of protection of the present disclosure.

Claims

1. A monolithically integrated square-FP coupled cavity laser array, characterized in that: include: A laser array, wherein each laser comprises a square whispering gallery microcavity angularly connected to the first end of a FP cavity, each of the square whispering gallery microcavities having different dimensions, and each of the FP cavities having the same dimensions, wherein the optical path length of the fundamental mode is varied by controlling the dimensions of the square whispering gallery microcavities to achieve equally spaced shifts in the lasing wavelength and equally spaced wavelength tuning of the laser array, and an electrical isolation slot is provided between the square whispering gallery microcavity and the FP cavity, allowing electrical injection to be performed separately between the square whispering gallery microcavity and the FP cavity; The multimode interference coupler is used to combine the lasers from the laser array and output them; A curved waveguide, one end of which is connected to the second end of the FP cavity, and the other end of which is connected to the multimode interference coupler; a gap is provided at the connection between the curved waveguide and the FP cavity, the length of the gap is 1-1.5 μm, and the width of the gap is the same as the width of the FP cavity.

2. The monolithically integrated square-FP coupled cavity laser array according to claim 1, characterized in that: The side lengths of the square whispering gallery microcavity form an arithmetic progression.

3. The monolithically integrated square-FP coupled cavity laser array according to claim 2, characterized in that: The interval g between each of the FP cavities is 250 μm.

4. The monolithically integrated square-FP coupled cavity laser array according to claim 3, characterized in that: The depth h of the square whispering gallery microcavity and FP cavity ranges from 4 to 5 μm.

5. The monolithically integrated square-FP coupled cavity laser array according to claim 1, characterized in that: The laser array includes four channels, eight channels, and sixteen channels.

6. The monolithically integrated square-FP coupled cavity laser array according to claim 1, characterized in that: The square whispering gallery microcavity includes an electric triggering structure.

7. The monolithically integrated square-FP coupled cavity laser array according to claim 1, characterized in that: The substrates of the square whispering gallery microcavity and the FP cavity include materials composed of group III and group V elements.

8. The monolithically integrated square-FP coupled cavity laser array according to claim 7, characterized in that: The active layers of the square whispering gallery microcavity and the FP cavity include one of quantum wells, quantum wires and quantum dots.

9. A method for preparing a monolithically integrated square-FP coupled cavity laser array according to any one of claims 1 to 8, characterized in that: include: S1. Photolithography a cavity on an epitaxial wafer, wherein the cavity includes a laser array, a multimode interference coupler, and a curved waveguide, wherein each laser in the laser array includes a square whispering gallery microcavity angularly connected to the first end of a FP cavity, each square whispering gallery microcavity has a different size, and each FP cavity has the same size; the multimode interference coupler is used to combine the lasers from the laser array and output them; one end of the curved waveguide is connected to the second end of the FP cavity, and the other end is connected to the multimode interference coupler; S2, continuing ICP etching the cavity; S3, BCB filling and etching; S4, etching an isolation groove between the square whispering gallery microcavity and the FP cavity; S5, evaporate electrodes to obtain a monolithic integrated square-FP coupled cavity laser array.

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