Traveling wave electrode photoelectric detector based on periodic loading and method for improving bandwidth

Abstract

The invention discloses a traveling wave electrode photoelectric detector based on periodic loading and a method for improving bandwidth. The traveling wave electrode photoelectric detector comprises a grating, a photoelectric detector, a traveling wave electrode, an adjustable resistor, a heating electrode and a power beam splitter. A GSG electrode is arranged at the input end of the traveling wave electrode, so that the traveling wave electrode forms a GSG traveling wave electrode, and an adjustable resistor is externally arranged on the GSG traveling wave electrode, so that the adjustable resistor is connected with the GSG electrode; the plurality of photoelectric detectors are fixedly positioned on the traveling wave electrode and are connected with the traveling wave electrode; the grating is connected with the power beam splitter and then is respectively connected with the plurality of photoelectric detectors; and the heating electrode is arranged on an optical transmission waveguide wire connected between the grating and each photoelectric detector. The GSG electrode external adjustable resistor is additionally arranged at the input end of the traveling wave electrode, and the heating resistor is arranged on an optical transmission waveguide wire of each path of detector to adjust the delay, so that when inevitable process tape-out and design errors exist, the impedance and the delay can be matched again through adjustment in two modes, and the bandwidth of the photoelectric detector is improved to the maximum extent.

Description

Technical Field

[0001] The invention relates to the technical field of microwave photonic devices, in particular to a travelling wave electrode photoelectric detector based on periodic loading and a method for improving bandwidth. Background Art

[0002] In the 1990s, microwave technology and light wave technology were combined to form a new cross-disciplinary field - microwave photonics (MWP). This discipline mainly studies how to use optoelectronic devices and methods to achieve the generation, transmission distribution, and processing of microwave / millimeter wave signals. Among them, photodetectors with high saturation output current and high bandwidth are important devices in microwave photonics, which can improve the gain, signal-to-noise ratio, and spurious-free dynamic range of analog optical links.

[0003] However, there is a trade-off between high saturation output current and high bandwidth for waveguide-type photodetectors (PD Photodetector). 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. However, when high optical 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. Therefore, the traveling-wave photodiodes (TWPD) are proposed to divide the high optical 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. At the same time, increasing the number of PDs increases the absorption area, achieving high saturation output current, and maintaining high bandwidth under the premise of speed matching and impedance matching.

[0004] TWPD adopts a periodic or non-periodic PD arrangement structure. Since the periodic symmetrical structure is relatively simpler to design than the non-periodic PD arrangement structure and it is easier to control the process error, most TWPDs adopt a periodic loading structure.

[0005] One problem with TWPD is that it generates photocurrent that propagates to the input end of the traveling wave electrode. Impedance matching is to connect a matching resistor (usually 50Ω) to the input end of the traveling wave electrode to eliminate the reflection of the photocurrent that propagates to the input end of the traveling wave electrode. Otherwise, the photocurrent that propagates to the input end of the traveling wave electrode will be completely reflected to the load end, and the phase difference generated with the photocurrent that propagates to the load end will limit the bandwidth.

[0006] However, due to process errors, the characteristic impedance of the actual transmission line is generally not 50Ω. Another problem is that the speeds of the optical signal and the RF (radio frequency) signal in the periodic distributed TWPD are different. The output port of the optical beam splitter and the PD array are connected through optical waveguide delay lines of different lengths (d1, d2, d3, d4...), so that the RF waves generated by different PDs are synchronized in the coplanar waveguide (CPW: coplanar waveguide) electrode. However, in actual applications, there are various effects in the waveguide line, and it is difficult to achieve complete speed matching.

[0007] In the prior art, the invention patent with the patent publication number CN107504987A discloses a method for improving the bandwidth of a traveling wave electrode photodetector based on non-periodic loading. When the traveling wave electrode input end of the TWPD is open, the transmission line with the effect of the capacitive load effect of the PD on the characteristic impedance of the transmission line and the increasing spacing between adjacent PDs is used to achieve the improvement of the bandwidth without sacrificing the output current. However, the problem of the impedance mismatch between the input end of the TWPD and the traveling wave resistor is not solved. Summary of the invention

[0008] The technical problem to be solved by the present invention is to solve the problem of mismatch between the speed of optical signal and electrical signal due to process errors, mismatch between input load and traveling wave resistor impedance and different speeds of optical signal and RF signal in periodically distributed TWPD.

[0009] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0010] A travelling wave electrode photoelectric detector based on periodic loading comprises: a grating (100), a photoelectric detector (200), a travelling wave electrode (300), an adjustable resistor (R1), a heating electrode (400) and a power beam splitter (500); a GSG electrode is arranged at the input end of the travelling wave electrode (300) so that the travelling wave electrode (300) forms a GSG travelling wave electrode (300a); an external adjustable resistor (R1) is arranged on the GSG travelling wave electrode (300a) so that the adjustable resistor (R1) is connected to the GSG electrode; a plurality of photoelectric detectors (200) are fixedly located on the travelling wave electrode (300) and connected to the travelling wave electrode (300); the grating (100) is connected to the power beam splitter (500) and then respectively connected to the plurality of photoelectric detectors (200); and the heating electrode (400) is on a light transmission waveguide (210) line connected between the grating (100) and each photoelectric detector (200).

[0011] Advantages: A variable resistor is connected to the input end of the traveling wave electrode of the TWPD through the GSG electrode. By adjusting the external resistor, the input load is completely matched with the traveling wave electrode impedance. Each optical waveguide is heated and adjusted to adjust the delay of the detector input optical signal so that the optical signal and the electrical signal are completely matched. Through two adjustment methods, the detector bandwidth is maximized.

[0012] In one embodiment of the present invention, a plurality of photodetectors (200) are on the traveling wave electrode (300), and the traveling wave electrode spacing between two adjacent photodetectors (200) is equal.

[0013] In one embodiment of the present invention, the length difference of the light transmission waveguides (210) of two adjacent photodetectors (200) is equal.

[0014] In one embodiment of the present invention, a GSG electrode is provided at the output end of the GSG traveling wave electrode (300a); a positive bias is applied to one end of the heat adjustment of the heating electrode (400), and the other end is connected to ground via a G electrode of the GSG electrode at the output end of the GSG traveling wave electrode (300a).

[0015] In one embodiment of the present invention, the distance between the traveling wave electrodes of two adjacent photodetectors (200) is 25-50 μm.

[0016] In one embodiment of the present invention, the length difference between the light transmission waveguides (210) of two adjacent photodetectors (200) is 25-50 μm.

[0017] In one embodiment of the present invention, two ends of the adjustable resistor (R1) are respectively connected to the G electrode and the S electrode of the GSG electrode.

[0018] A method for improving the bandwidth of a traveling wave electrode photodetector based on periodic loading, which is used for the traveling wave electrode photodetector described above, comprises the following steps:

[0019] S100, an optical signal is coupled into an optical transmission waveguide (210) through a grating (100), and is split through a power beam splitter (500) to generate multiple input optical signals of equal power;

[0020] S200, designing to make the distance between the traveling wave electrodes of two adjacent photodetectors (200) equal and the length difference between the adjacent light transmission waveguides (210) before entering the photodetectors (200) equal; and adjusting the effective refractive index of the light transmission waveguide (210) and the speed of the light signal by heating the electrode (400) so that the radio frequency waves generated by different photodetectors (200) are synchronized in the coplanar waveguide electrode;

[0021] S300, at the electrical signal transmission end, adjust the adjustable resistor (R1) to make the input impedance Zin Equal to the characteristic impedance Z of the transmission line c , so that the reflection coefficient is 0.

[0022] Compared with the prior art, the beneficial effects of the present invention are: an external adjustable resistor of the GSG electrode is added to the input end of the traveling wave electrode, and the delay is adjusted by heating the optical transmission waveguide of each detector. In this way, when inevitable process flow and design errors exist, the impedance and delay can still be adjusted in two ways to match each other, thereby maximizing the bandwidth of the photodetector. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Schematic diagram of a traveling wave electrode photodetector based on periodic loading according to an embodiment of the present invention.

[0024] Figure 2 FIG. 4 is a simplified schematic diagram of a multi-stage PD according to an embodiment of the present invention.

[0025] Figure 3 For the embodiment of the present invention Figure 1 Schematic diagram of the BB cross section.

[0026] Figure 4 For the embodiment of the present invention Figure 1 Schematic diagram of the AA section. DETAILED DESCRIPTION

[0027] In order to facilitate those skilled in the art to understand the technical solution of the present invention, the technical solution of the present invention is further described in conjunction with the accompanying drawings of the specification.

[0028] The terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of the features. In the description of this application, the meaning of "plurality" is two or more, unless otherwise clearly and specifically defined.

[0029] See also Figure 1As shown, the present invention provides a traveling wave electrode photodetector based on periodic loading, comprising a grating 100, a photodetector 200, a traveling wave electrode 300, an adjustable resistor R1, a heating electrode 400 and a power beam splitter 500. A GSG electrode is arranged at the input end of the traveling wave electrode 300, so that the traveling wave electrode 300 forms a GSG traveling wave electrode 300a, and an external adjustable resistor R1 is arranged on the GSG traveling wave electrode 300a, so that the adjustable resistor R1 is connected to the GSG electrode. A plurality of photodetectors 200 are fixedly located on the traveling wave electrode 300 and connected to the traveling wave electrode 300. After the grating 100 is connected to the power beam splitter 500, it is respectively connected to the plurality of photodetectors 200; the heating electrode 400 is on the optical transmission waveguide 210 line connected between the grating 100 and each photodetector 200. A GSG electrode and an external adjustable resistor R1 are added to the input end of the traveling wave electrode 300, and a heating electrode 400 is added to the optical transmission waveguide 210 line of each photodetector 200 to adjust the delay. In this way, when inevitable process flow and design errors exist, the impedance and delay can still be adjusted in two ways to match each other, thereby maximizing the bandwidth of the photodetector.

[0030] In one embodiment of the present invention, a plurality of photodetectors 200 are on the traveling wave electrode 300, and the traveling wave electrode spacing between two adjacent photodetectors 200 is equal. The length difference of the light transmission waveguide 210 of two adjacent photodetectors 200 is equal. Specifically, the traveling wave electrode spacing is 25-50 μm, and the length difference of the light transmission waveguide 210 is 25-50 μm.

[0031] The output end of the GSG traveling wave electrode 300a is provided with a GSG electrode, and the heat adjustment end of the heating electrode 400 is positively biased, and the other end is connected to the G electrode of the GSG electrode on the output end of the GSG traveling wave electrode 300a and grounded.

[0032] See also Figure 1 As shown, in one embodiment of the present invention, an external laser passes through the optical waveguide input end. At the input end of the strip waveguide 220, the optical signal is coupled into the strip waveguide 220 through the grating 100, and a multi-stage one-to-two MMI power splitter or a Y-type power splitter is used for splitting to generate multiple input optical signals of equal power.

[0033] In order to ensure the speed matching between the group velocity Vg of the optical signal and the speed Ve of the electrical signal, the effective refractive index of the waveguide is changed by thermal adjustment of the heating electrode 400, thereby adjusting the transmission speed of the optical signal. The reflected RF wave is absorbed by the adjustable resistor R1. Finally, the photocurrent is output by the adjacent photodetector 200 and the GSG traveling wave electrode 300a. In this embodiment, only four photodetectors 200 are listed in the figure for simplicity, and the specific number is set according to the requirements.

[0034] See also Figure 1 and Figure 2 As shown, in one embodiment of the present invention, Δ1, Δ2, Δ3 are the spacings between the transmission lines PD1, PD2, PD3 and PD4. Because the present invention is a periodic TWPD, Δ1 = Δ2 = Δ3. d1, d2, d3 are the length differences between adjacent optical waveguides before entering PD1, PD2, PD3 and PD4. In order to ensure the speed matching between the group velocity Vg of the optical signal and the speed Ve of the electrical signal, the difference between adjacent waveguides is also equal, that is, d1 = d2 = d. Itot is the output current; Rload is the load.

[0035] In this embodiment, each photodetector 200 as a current source provides a photocurrent propagating to the input end and the load end of the GSG traveling wave electrode 300a, such as PD2, and the photocurrent propagating to the input end and the load end of the GSG traveling wave electrode 300a are Ib2 and If2 respectively. The input end of the GSG traveling wave electrode 300a is externally connected to an adjustable resistor R1, and the photocurrent propagating to the input end of the GSG traveling wave electrode 300a will be completely absorbed by the adjustable resistor R1, and impedance matching is achieved by adjusting the adjustable resistor R1. Eliminate the limitation of the bandwidth on the phase lag between the current propagating to the input end and the load end of the GSG traveling wave electrode 300a.

[0036] In this embodiment, by connecting a heating electrode 400 to each waveguide, the effective refractive index of the waveguide is changed by thermal adjustment of the heating electrode 400. When the heating electrode 400 is heated by the thermal adjustment, due to the thermo-optical effect, the refractive index of the waveguide below the heating electrode changes due to the heat: n(T) = n0 + α(T), α is the thermo-optical coefficient of the material, T represents the temperature, n(T) represents the refractive index when the temperature is T, and n0 represents the refractive index at room temperature 300K. Then the transmission group velocity Vg of the optical signal is adjusted to C / n(T), where C is the speed of light, to ensure the speed matching between the group velocity Vg of the optical signal and the speed Ve of the electrical signal. That is: dn / Vg = Δn / Ve, where dn represents the length difference between the nth optical transmission waveguide and the n-1th optical transmission waveguide, and Δn represents the distance between the traveling wave electrodes. The RF waves generated by different photodetectors 200 are synchronized in the CPW electrode to improve the bandwidth.

[0037] In order to minimize the device area, limited by the structure and size of the photodetector 200 and the design requirements of the coupled optical waveguide, the traveling wave electrode spacing between the photodetectors 200 is 40μm, the path difference of each waveguide is 40μm, a heating electrode 400 is added to each optical waveguide, an adjustable resistor is externally connected to the input end of the CPW electrode, the widths of the GSG traveling wave electrodes 300a are 50, 7, and 50μm respectively, and the GS electrode spacing is 4μm.

[0038] See also Figure 3As shown, in one embodiment of the present invention, the GSG traveling wave electrode 300a is prepared based on SOI material. The SOI material is composed of bottom silicon 310, silicon dioxide substrate 320, strip waveguide layer 330 and silicon dioxide cladding 340, and a through-hole 341 is formed in the silicon dioxide cladding 340, and a Ge layer 342 is provided in the silicon dioxide cladding 340 and the strip waveguide layer 330. The GSG electrode is provided on the silicon dioxide cladding 340.

[0039] See also Figure 4 As shown, in one embodiment of the present invention, the GSG traveling wave electrode 300a is a two-layer dielectric structure, according to the thickness of the bottom silicon h1, the thickness of the silicon dioxide substrate h2, the G electrode width Wg, the S electrode width W, the electrode spacing S, and the electrode thickness t of the GSG electrode. Table 1 shows the structural parameters of the two-layer dielectric structure of the GSG traveling wave electrode 300a.

[0040] Table 1. Structural parameters of the two-layer dielectric structure of the GSG traveling wave electrode

[0041]

[0042] See also Figure 1 and Figure 2 As shown, the present invention also provides a method for improving the bandwidth of a traveling wave electrode photodetector based on periodic loading, using the above-mentioned traveling wave electrode photodetector, comprising the following steps:

[0043] S100, the optical signal is coupled into the optical transmission waveguide 210 through the grating 100, and is split by the power beam splitter 500 to generate multiple input optical signals of equal power.

[0044] In this embodiment, when the input end of the GSG traveling wave electrode 300a is externally connected to an adjustable resistor R1, the external laser enters the 220nm thick strip waveguide 220 through the grating 100 at the input end of the optical waveguide, and then enters the optical transmission waveguide 210 with a waveguide path difference of 40μm in each path through the two-stage 1x2 MMI power splitter.

[0045] S200 is designed to make the distance between the traveling wave electrodes of two adjacent photodetectors 200 equal and the length difference between the adjacent optical transmission waveguides 210 before entering the photodetector 200 equal; and by heating the electrode 400, the effective refractive index of the optical transmission waveguide 210 is adjusted, and the speed of the optical signal is adjusted so that the radio frequency waves generated by different photodetectors 200 are synchronized in the coplanar waveguide electrode.

[0046] In this embodiment, as the number of photodetectors 200 increases, in order to ensure the speed matching between the group velocity Vg of the optical signal and the velocity Ve of the electrical signal, the traveling wave electrode spacing between adjacent photodetectors 200 and the length difference between adjacent optical transmission waveguides 210 before entering the photodetector 200 are designed. Since the present invention is based on periodic TWPD design, the length difference between the two adjacent optical transmission waveguides 210 is equal, and the distance between adjacent photodetectors 200 is equal.

[0047] S300, at the electrical signal transmission end, adjust the adjustable resistor R1 so that the input impedance Z in Equal to the characteristic impedance Z of the transmission line c , so that the reflection coefficient is 0.

[0048] In this embodiment, at the receiving end, the input end of the GSG traveling wave electrode 300a is connected to an adjustable resistor R1 through the GSG electrode, and the current propagating to the input end of the traveling wave electrode 300a is absorbed by the adjustable resistor R1 at the input end of the traveling wave electrode 300a, which is completely matched with the impedance of the traveling wave electrode 300a. By adjusting the adjustable resistor R1, the input end impedance Z in Equal to the characteristic impedance Z of the transmission line c , the reflection coefficient is 0. The limitation of the bandwidth caused by the phase lag between the current propagating to the input end and the load end of the traveling wave electrode 300 is eliminated, thereby maximizing the bandwidth.

[0049] In the traditional traveling wave detector, due to the existence of process errors, the impedance Z at the input end of the traveling wave electrode is in Not equal to the characteristic impedance Z of the transmission line c When , the backward propagating RF wave will be reflected at the input end of the traveling wave electrode, and the expression of the reflection coefficient Гin is:

[0050] It is obvious to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the spirit or essential features of the present invention. Therefore, the embodiments should be regarded as exemplary and non-limiting from any point of view, and the scope of the present invention is defined by the appended claims rather than the above description, and it is intended that all changes falling within the meaning and scope of the equivalent elements of the claims are included in the present invention, and any reference numerals in the claims should not be regarded as limiting the claims involved.

[0051] The above-described embodiments merely represent implementation methods of the invention. The protection scope of the present invention is not limited to the above-described embodiments. For those skilled in the art, several modifications and improvements may be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention.

Claims

1. A travelling wave electrode photodetector based on periodic loading, characterized in that: include: A grating (100), a photodetector (200), a traveling wave electrode (300), an adjustable resistor (R1), a heating electrode (400) and a power beam splitter (500); a GSG electrode is arranged at the input end of the traveling wave electrode (300) so that the traveling wave electrode (300) forms a GSG traveling wave electrode (300a); an adjustable resistor (R1) is externally arranged on the GSG traveling wave electrode (300a) so that the adjustable resistor (R1) is connected to the GSG electrode; A plurality of photodetectors (200) are fixedly located on a traveling wave electrode (300) and connected to the traveling wave electrode (300); the grating (100) is connected to a power beam splitter (500) and then respectively connected to the plurality of photodetectors (200); and the heating electrode (400) is on a light transmission waveguide (210) line connected between the grating (100) and each photodetector (200).

2. The traveling wave electrode photodetector based on periodic loading according to claim 1, characterized in that: A plurality of photodetectors (200) are on a traveling wave electrode (300), and the traveling wave electrode spacings between two adjacent photodetectors (200) are equal.

3. The traveling wave electrode photodetector based on periodic loading according to claim 2, characterized in that: The length difference of the light transmission waveguides (210) of two adjacent photodetectors (200) is equal.

4. The traveling wave electrode photodetector based on periodic loading according to claim 1, characterized in that: The output end of the GSG traveling wave electrode (300a) is provided with a GSG electrode; A positive bias voltage is applied to one end of the heat adjustment of the heating electrode (400), and the other end is grounded by being connected to the G electrode of the GSG electrode at the output end of the GSG traveling wave electrode (300a).

5. The traveling wave electrode photodetector based on periodic loading according to claim 2, characterized in that: The distance between the traveling wave electrodes of two adjacent photodetectors (200) is 25-50 μm.

6. The traveling wave electrode photodetector based on periodic loading according to claim 3, characterized in that: The length difference between the light transmission waveguides (210) of two adjacent photodetectors (200) is 25 to 50 μm.

7. The traveling wave electrode photodetector based on periodic loading according to claim 1, characterized in that: The two ends of the adjustable resistor (R1) are connected to the G electrode and the S electrode of the GSG electrode respectively.

8. A method for improving the bandwidth of a traveling wave electrode photodetector based on periodic loading, characterized in that: The traveling wave electrode photoelectric detector according to any one of claims 1 to 7 comprises the following steps: S100, an optical signal is coupled into an optical transmission waveguide (210) through a grating (100), and is split through a power beam splitter (500) to generate multiple input optical signals of equal power; S200, designing to make the distance between the traveling wave electrodes of two adjacent photodetectors (200) equal and the length difference between the adjacent light transmission waveguides (210) before entering the photodetectors (200) equal; and adjusting the effective refractive index of the light transmission waveguide (210) and the speed of the light signal by heating the electrode (400) so that the radio frequency waves generated by different photodetectors (200) are synchronized in the coplanar waveguide electrode; S300, at the electrical signal transmission end, adjust the adjustable resistor (R1) to make the input impedance Z in Equal to the characteristic impedance Z of the transmission line c , so that the reflection coefficient is 0.

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