Traveling wave photoelectric detector with annular axisymmetric structure

Abstract

The traveling wave photoelectric detector comprises a plurality of PDs which are evenly distributed on an annular transmission line, the two ends of the annular transmission line are connected with GSG traveling wave electrodes, and the whole annular transmission line is of an axial symmetry structure. An optical signal enters the optical waveguide through the grating coupler at the input end of the optical waveguide, and the optical waveguide adopts a multi-stage one-to-two power beam splitter to split light and is connected to the PD; the GSG traveling wave electrode two-layer dielectric structure comprises a silicon substrate and a silicon dioxide layer growing on the top of the silicon substrate, the upper portion of the silicon dioxide layer is a thin silicon layer, and the thin silicon layer is covered with two silicon dioxide layers. A ground electrode of the GSG traveling wave electrode is connected with a first metal layer M1 through a through hole, and a signal electrode of the GSG traveling wave electrode is connected with a second metal layer M2 through a through hole. Additional process steps are not needed, processing is easy, the method is perfectly compatible with the CMOS process, and the bandwidth, the saturation output power and the overall performance of the device can be improved at the same time.

Description

Technical Field

[0001] The invention relates to the technical field of silicon-based optoelectronic devices, in particular to a traveling wave photoelectric detector with an annular axisymmetric structure. Background Art

[0002] Microwave photonics has been an interesting and promising research field for decades with many potential applications. Recently, there has been extensive research and development in the field of integrated microwave photonics. For integrated microwave photonic systems, it is often necessary to realize various high-performance photonic devices. Among them, high-power photodetectors, as indispensable components for photoelectric conversion, are extremely important. Increasing the PD output photocurrent helps to improve the key performance indicators of microwave photonic links, including link gain, spurious-free dynamic range, and noise figure.

[0003] However, it is very difficult to increase the saturation output power of waveguide-type high-speed photodetectors without reducing their bandwidth. In order to ensure that the capacitance and carrier transit time are small, waveguide-type high-speed photodetectors have only a small absorption area, so they can achieve high bandwidth; but when high light power is input, due to the small absorption area, the space charge effect and thermal failure of waveguide-type high-speed photodetectors will limit the high saturation output current. The traveling wave electrode photodetector proposes to divide the high light power input light into multiple beams of low-power light through a power divider to reduce the impact of space charge effect and thermal failure, while increasing the number of PDs to increase the absorption area, achieve high saturation output current, and maintain high bandwidth under the premise of speed matching and impedance matching.

[0004] Traditional traveling wave photodetectors are limited by three factors, namely impedance matching conditions, speed matching conditions, and TL (transmission line) microwave losses. A matching resistor is connected to the input end of the traveling wave electrode to eliminate the photocurrent propagating to the input end of the traveling wave electrode. Otherwise, the photocurrent propagating to the input end of the traveling wave electrode will be completely reflected to the load end, and the phase difference with the photocurrent propagating to the load end will cause the bandwidth to decrease. Although connecting a resistor matching the output end to the input end increases the bandwidth, half of the output photocurrent is wasted on the matching impedance at the input end. On the other hand, in order to reduce the transmission line loss, the transmission line should not be designed to be too long, which limits the number of PD units and is not conducive to the increase of saturated output power. Summary of the invention

[0005] The object of the present invention is to provide a traveling wave photoelectric detector with an annular axisymmetric structure to solve the problems raised in the above background technology.

[0006] To achieve the above object, the present invention provides the following technical solution: a traveling wave photodetector with an annular axisymmetric structure, comprising a plurality of PDs, grating couplers and beam splitters uniformly distributed on an annular transmission line, wherein both ends of the annular transmission line are connected to a common GSG electrode, and the overall structure is an axisymmetric structure;

[0007] Specifically, 2n PD units are evenly distributed on a ring transmission line, and both ends of the ring transmission line are connected to GSG electrodes, forming an axisymmetric structure as a whole. This axisymmetric structure provides design freedom while ensuring the simplicity of the design. Compared with traditional traveling wave photodetectors, this design has the following advantages:

[0008] 1. The backward propagating photocurrent no longer needs to be reflected, and the path to the GSG signal electrode is shortened, significantly reducing the transmission line loss.

[0009] 2. No impedance matching is required to absorb the backward propagating photocurrent, which greatly improves the saturated output power.

[0010] 3. The axisymmetric structure ensures the signal delay matching of each PD in forward and backward transmission, greatly improving the device bandwidth;

[0011] This new structure detector does not require additional process steps, is easy to process, and is perfectly compatible with CMOS technology. It can simultaneously improve the bandwidth, saturated output power and overall performance of the device.

[0012] The external laser enters the optical waveguide through the grating at the input end of the optical waveguide, and the optical waveguide uses a multi-stage one-to-two power beam splitter to split the light and is connected to the PD;

[0013] The two-layer dielectric structure of the GSG traveling wave electrode includes a substrate silicon and a buried silicon dioxide layer located on the top of the substrate silicon, the top of the buried silicon dioxide layer is covered with a thin silicon layer (part of the region is epitaxially grown with a germanium absorption region), and the thin silicon layer is covered with a silicon dioxide cladding layer;

[0014] The ground electrode of the GSG traveling wave electrode is connected to the first metal layer M through a through hole. 1 , through the first metal layer M 1 Connect to the terminal, and then connect to the M 2 The signal electrode of the GSG traveling wave electrode is connected to the first metal layer M through a through hole. 1 connected, and then connected to the second metal layer M through a through hole 2 , and then by the second layer of metal M 2 Access terminal.

[0015] Preferably, the power beam splitter is a 1x2 MMI or Y-type power beam splitter.

[0016] Preferably, the thickness of the optical waveguide is 220 nm, and the path difference between every two adjacent optical waveguide delay lines and the spacing between two PD coplanar waveguides satisfy delay matching.

[0017] Preferably, the widths of the GSG traveling wave electrodes are 50 μm, 7 μm, and 50 μm, respectively, and the GS electrode spacing is 4 μm.

[0018] Preferably, between the two silicon dioxide layers is a silicon layer and a germanium absorption region epitaxially extended in a partial area.

[0019] Preferably, the first metal layer M 1 The electrode material is Cu, and the second metal layer M 2 The electrode material is AlCu.

[0020] Specifically, the photocurrent entering the PD unit will be transmitted forward and backward; compared with the traditional traveling wave photodetector, the annular symmetrical design enables the photocurrent transmitted backward to be directly absorbed by the signal electrode without reflection and then passing through the PD to be absorbed by the signal electrode. The path of the backward propagating photocurrent to reach the GSG signal electrode is shortened, which significantly reduces the transmission line loss;

[0021] The ring-shaped symmetrical design enables the backward-transmitted photocurrent to be directly connected to the load end without setting up impedance matching to absorb the backward-transmitted photocurrent, which can improve the bandwidth without sacrificing the output current;

[0022] As the number of PDs increases, in order to ensure the group velocity V of the optical signal g The speed of the electrical signal V e To match, it is necessary to design the spacing between adjacent PDs and the length difference between adjacent waveguides before entering the PDs. In the present invention, 2n PDs are evenly and symmetrically distributed on the ring transmission line, the spacing between adjacent PDs is equal, and the length difference between adjacent waveguides before entering the PDs is also equal. It is only necessary to design the appropriate PD spacing and length difference once, which greatly reduces the complexity of the design.

[0023] The specific steps of the present invention are as follows:

[0024] Step 1) Determine the number of PD units 2n according to demand, determine the appropriate ring radius, and evenly and symmetrically distribute the PD units on the ring transmission line;

[0025] Step 2) To ensure the group velocity V of the optical signal g and the speed of the electrical signal V e The matching between the adjacent PDs and the length difference between the adjacent waveguides before entering the PDs are designed. The path difference between each two adjacent optical waveguide delay lines and the coplanar waveguide spacing between the two PDs satisfy the delay matching. In the present invention, thanks to the axially symmetrical structure, the length difference between the two adjacent waveguides is equal, and the distance between adjacent PDs is equal.

[0026] Step 3) When the two ends of the ring transmission line are connected to the traveling wave electrodes, at the input end of the optical waveguide, the external laser enters the optical waveguide through grating coupling, and a multi-stage one-to-two MMI or Y-type power beam splitter is used for light splitting, generating multiple equal-power input optical signals entering each PD;

[0027] Step 4) The ground electrode of the PD is connected to the first metal layer M through the through hole. 1 , the transmission line of the entire ground electrode is at M 1 The signal electrode of the GSG traveling wave electrode is connected to the first metal M through a through hole at the terminal, and finally connected to the PAD. 1 connected, and then connected to the second metal layer M through a through hole 2 The transmission line of the entire signal electrode is at M 2 Then M 2 Directly enter the terminal PAD.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] 1. No need to add additional process steps, easy processing, and perfect compatibility with CMOS process; the axisymmetric structure makes the waveguide and transmission line design simpler.

[0030] 2. The backward propagating photocurrent is absorbed by the GSG signal electrode more quickly, significantly reducing the transmission line loss.

[0031] 3. No impedance matching is required to absorb the backward propagating photocurrent, which greatly improves the saturated output power.

[0032] 4. The symmetrical structure ensures that the RF signals transmitted forward and backward by each PD are delayed matched, greatly improving the device bandwidth. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 It is the overall framework diagram of the annular axisymmetric traveling wave photodetector of the present invention (the remaining PDs are represented by ellipsis).

[0034] Figure 2 It is a simplified schematic diagram of the annular axisymmetric traveling wave photodetector of the present invention (the remaining PDs are represented by ellipsis).

[0035] Figure 3 This is a lateral interface diagram of the PD unit.

[0036] In the figure: 1, grating, 2, 220nm thick optical waveguide, 3, power beam splitter, 4, PD (photodetector), 5, GSG traveling wave electrode, 6, substrate silicon, 7, silicon dioxide buried layer, 8, germanium (Ge), 9, silicon dioxide cladding, 10, through hole, 11, first metal layer M 1 , 12, the second metal layer M 2 . DETAILED DESCRIPTION

[0037] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0038] See also Figure 1-3 The present invention provides a technical solution: a traveling wave photodetector with an annular axisymmetric structure, including a plurality of PDs evenly distributed on an annular transmission line, grating coupling and a beam splitter, GSG electrodes 5 are connected to both ends of the annular transmission line, and the overall structure is axisymmetric; compared with traditional traveling wave photodetectors, this design has the following advantages: 1. The backward propagating photocurrent does not need to be reflected, so the path of the GSG signal electrode is shortened, and the transmission line loss is significantly reduced. 2. There is no need to set impedance matching to absorb the backward propagating photocurrent, which greatly improves the saturated output power. 3. The axisymmetric structure ensures the signal delay matching of each PD for forward and backward transmission, which greatly improves the device bandwidth. This new structure detector does not require additional process steps, is easy to process, is perfectly compatible with CMOS technology, and can simultaneously improve the bandwidth, saturated output power and overall performance of the device.

[0039] The optical signal enters the optical waveguide 2 through the grating 1 at the input end, and the optical waveguide 2 uses a multi-stage one-to-two power beam splitter 3 to split the light and connect it to each PD;

[0040] The two-layer dielectric structure of the GSG traveling wave electrode 5 includes a bottom silicon 6 and a silicon dioxide substrate 7 mounted on the top of the bottom silicon 6, and a silicon dioxide cladding 9 is mounted on the top of the silicon dioxide substrate 7;

[0041] The ground electrode of the GSG traveling wave electrode 5 is connected to the first metal layer M through the through hole 10. 1 11, the signal electrode of the GSG traveling wave electrode 5 is connected to the second metal layer M through the through hole 10 2 12.

[0042] In the present invention, the power beam splitter is a 1x2 MMI or Y-type power beam splitter.

[0043] In the present invention, the thickness of the optical waveguide 2 is 220 nm, and the path difference between every two adjacent optical waveguide delay lines and the distance between two PD coplanar waveguides satisfy the delay matching.

[0044] In the present invention, the widths of the GSG traveling wave electrodes 5 are 50 μm, 7 μm, and 50 μm, respectively, and the GS electrode spacing is 4 μm.

[0045] In the present invention, germanium 8 is epitaxially grown in the silicon dioxide cladding layer 9 as a light absorbing material.

[0046] In the present invention, the first metal layer M 1 The electrode material is Cu, and the second metal layer M 2 The electrode material is AlCu.

[0047] The specific steps of the present invention are as follows:

[0048] Step 1) Determine the number of PD units 2n according to demand, determine the appropriate ring radius, and evenly and symmetrically distribute the PD units on the ring transmission line;

[0049] Step 2) To ensure the group velocity V of the optical signal g and the speed of the electrical signal V e The matching between the adjacent PDs and the length difference between the adjacent waveguides before entering the PDs are designed, and the path difference between each two adjacent optical waveguide delay lines and the coplanar waveguide spacing between the two PDs meet the delay matching. In the present invention, thanks to the axially symmetrical structure, the length difference between the two adjacent waveguides is equal, and the distance between adjacent PDs is equal;

[0050] Step 3) When the two ends of the ring transmission line are connected to the traveling wave electrodes, at the input end of the optical waveguide, the external laser enters the optical waveguide through grating coupling, and a multi-stage one-to-two MMI or Y-type power beam splitter is used for light splitting, generating multiple equal-power input optical signals entering each PD;

[0051] Step 4) The ground electrode of each detector is first connected to the first metal layer M through a through hole 1 , the transmission line of the entire ground electrode is at M 1 In the process, the signal electrodes of each PD are first connected to the first metal layer M through a through hole. 1 , and then connected to the second metal layer M through a through hole 2 The transmission line of the entire signal electrode is at M 2 middle;

[0052] like Figure 1As shown, in the present invention, an external laser enters a 220nm thick optical waveguide 2 through a grating 1 at the input end of the optical waveguide, and then the light is equally divided into 8 parts through a four-stage 1x2 MMI 3 and enters each optical waveguide with the same waveguide path difference. When the light enters the PD, a part of the photocurrent is directly transmitted to the signal electrode, and the other part propagates in the reverse direction and is subsequently absorbed by the signal electrode. Compared with a traditional traveling wave photodetector, the backward propagating photocurrent does not need to be reflected or absorbed by a matching impedance, but is directly absorbed by the signal electrode. Finally, the GSG traveling wave electrode 5 outputs the photocurrent.

[0053] like Figure 2 The figure shows a simplified schematic diagram of the present invention. For simplicity, only 8 PD units are listed in the figure, which are numbered ①-⑧ in the counterclockwise direction. Δ is the transmission distance between PD No. ① and the signal electrode, and d is the distance between adjacent PDs. Thanks to the axisymmetric structure, the transmission distance between PD No. ⑧ and the signal electrode is also Δ, and the distance d between adjacent PDs is also equal. In order to ensure the group velocity V of the optical signal g and the speed of the electrical signal V e The velocities between them are matched and the differences between adjacent waveguides are also equal.

[0054] like Figure 2 As shown, each PD acts as a current source, generating photocurrents in both clockwise and counterclockwise directions. For example, the counterclockwise current generated by PD No. ② is I 1 , the clockwise current is I 2 The photocurrent propagating clockwise does not need to be reflected back and then pass through PD ② to reach the signal electrode, but is directly absorbed by the signal electrode in the clockwise direction, thereby reducing the transmission loss. When the photocurrent propagation speed is V g When 1 The time required to propagate to the signal electrode is t 1 = (d+Δ) / V g , and the time t for the reverse photocurrent to propagate to the signal level 2 = (6d+Δ) / V g Compared with the traditional traveling wave detector structure, the absorption speed of the reverse signal is greatly improved. Due to the axisymmetric structure, the time for the clockwise photocurrent of PD No. 7, which is symmetrical with PD No. 2, to reach the signal electrode is (d+Δ) / V, that is, t 1 ; The time it takes for the counterclockwise photocurrent to reach the signal electrode is (6d+Δ) / V, i.e., t 2 Similar to other PDs, this structure greatly improves the delay matching. While increasing the device bandwidth, it also maintains a high saturated output power.

[0055] The present invention can adjust the number of PD units according to user needs and determine the appropriate annular radius according to the number of PD units, so that the PDs can be evenly and symmetrically distributed on the annular waveguide line. The widths of the traveling wave electrodes GSG are 50μm, 7μm, and 50μm respectively, and the GS electrode spacing is 4μm.

[0056] like Figure 3 As shown, the present invention is based on SOI material (SOI material is composed of substrate silicon 6, silicon dioxide buried layer 7, 220nm thick optical waveguide 2 and silicon dioxide cladding 9), the thickness of substrate silicon 6 is h 1 , the thickness of the silicon dioxide layer 7 h 2 , the first metal layer M 1 Thickness 3 The electrode widths W and W of the GSG traveling wave electrode 5 are g , electrode spacing S, electrode thickness t. Table 1 shows the structural parameters related to the PD unit.

[0057] like Figure 2 , Figure 3 As shown, the ground electrode connected to the black waveguide is connected to the first metal layer M through a through hole. 1 The signal electrode connected by the white waveguide is connected to the second metal layer M through a through hole. 2 .

[0058] Table 1. PD unit related structural parameters

[0059]

[0060] The contents not described in detail in this specification belong to the prior art known to professional and technical personnel in the field. Although the embodiments of the present invention have been shown and described, it is understood by ordinary technicians in the field that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principle and spirit of the present invention. The scope of the present invention is defined by the attached claims and their equivalents.

Claims

1. A traveling wave photodetector with an annular axisymmetric structure, Features: It comprises a plurality of PDs (4) uniformly distributed on a ring-shaped transmission line, wherein two ends of the ring-shaped transmission line are connected to GSG traveling wave electrodes (5), and the whole has an axisymmetric structure; The optical signal enters the optical waveguide (2) through the grating (1) at the input end of the optical waveguide, and the optical waveguide (2) uses a multi-stage one-to-two power beam splitter (3) to split the light and connect it to the PD (4); The two-layer dielectric structure of the GSG traveling wave electrode (5) comprises a substrate silicon (6) and a silicon dioxide buried layer (7) located on the top of the substrate silicon (6), the top of the silicon dioxide buried layer (7) is covered with a thin silicon layer, and the thin silicon layer is covered with a silicon dioxide cladding layer (9); The ground electrode of the GSG traveling wave electrode (5) is connected to the first metal layer M through a through hole (10). 1 (11), through the first metal layer M 1 (11) Connect to the terminal, and then connect to M through the through hole at the terminal. 2 (12) connected; the signal electrode of the GSG traveling wave electrode (5) is connected to the first metal layer M through the through hole (10) 1 (11) connected, and then connected to the second metal layer M through a through hole 2 (12), and then the second metal layer M 2 (12) Access terminal.

2. The traveling wave photoelectric detector of the annular axisymmetric structure according to claim 1, Features: The power beam splitter is a 1x2 MMI or Y-type power beam splitter.

3. The traveling wave photoelectric detector of the annular axisymmetric structure according to claim 1, Features: The thickness of the optical waveguide (2) is 220 nm, and the path difference between every two adjacent optical waveguide delay lines and the spacing between two PD (4) coplanar waveguides satisfy the delay matching.

4. The traveling wave photoelectric detector of the annular axisymmetric structure according to claim 1, Features: The widths of the GSG traveling wave electrodes (5) are 50 μm, 7 μm and 50 μm respectively, and the distance between the GS electrodes is 4 μm.

5. The traveling wave photoelectric detector of the annular axisymmetric structure according to claim 1, Features: Germanium (8) is arranged in the silicon dioxide cladding (9).

6. The traveling wave photoelectric detector of the annular axisymmetric structure according to claim 1, Features: The first metal layer M 1 (11) The electrode material is Cu, and the second metal layer M 2 (12) The electrode material is AlCu.

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