Ultrahigh bandwidth photoelectric detector based on thin film lithium niobate platform

Abstract

An epitaxial layer is deposited and grown on a semi-insulating InP substrate, and the epitaxial layer sequentially comprises a p-type contact layer, an absorption layer, an InGaAsP quaternary layer, a cliff layer, a drift layer and an n-type contact layer; the InP wafer is bonded with the thin-film lithium niobate TFLN to form a configuration that the n region is in the lower part and the p region is in the upper part, so that the resistance is effectively reduced; the p-type contact layer is made of heavily doped InGaAs; and the n-type contact layer is a heavily doped n-type InP layer. According to the invention, the bandwidth of 130 GHz and the photoelectric responsivity of 0.35 A / W are shown, and the application potential in a high-speed and high-capacity communication system is huge.

Description

Technical Field The present invention belongs to the field of photoelectric detection, and in particular relates to an ultra-high bandwidth photoelectric detector based on a thin film lithium niobate platform. Background Art Rapidly developing fields such as cloud computing and artificial intelligence require efficient, low-cost ultra-large capacity and large-scale data processing. Integrated photonic technology is seen as a potential solution to meet these needs due to its large bandwidth, low power consumption and scalability [1]. Thin-film lithium niobate (TFLN) has been widely studied due to its high electro-optic coefficient, wide transparency window and high refractive index contrast [2], [3]. The realization of a high-speed and multifunctional integrated photonic platform requires that all devices on the chip have large bandwidth and excellent performance. Among them, high-speed and efficient electro-optic modulation has achieved remarkable results [4]. Tunable narrow-linewidth III-V lasers integrated on a thin-film lithium niobate platform have been reported [5]. Similarly, broadband heterogeneous integrated photodetectors (PDs) have also been realized on a thin-film lithium niobate platform. Recently, by using SU-8 as a bonding layer and bonding III-V chips to thin-film lithium niobate using a die bonding technique, a high-speed photodetector with a bandwidth of 80 GHz was prepared, and the reception of 40 Gbit / s on-off keying signals was achieved [6]. In our previous research, we used wafer bonding technology to bond III-V wafers to thin-film lithium niobate wafers to fabricate broadband photodetectors with a bandwidth of 110 GHz, and achieved error-free demodulation of 10, 20, and 32 Gbaud four-level pulse amplitude modulation (PAM4) signals in back-to-back (B2B) communication systems, corresponding to a maximum rate of 64 Gbit / s [7]. Although photodetectors on thin-film lithium niobate have achieved bandwidths exceeding 100 GHz, their potential for receiving high data rate signals in high-speed communication systems has not yet been verified. References:

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[0007] C. Wei et al., “Ultra-wideband Waveguide-coupled Photodiodes Heterogeneously Integrated on a Thin-film Lithium Niobate Platform,” Light: Advanced Manufacturing, vol. 4, no. 3, p. 1, 2023. Summary of the Invention In order to further improve the bandwidth of the detector, the present invention provides an ultra-high bandwidth photoelectric detector based on a thin film lithium niobate platform. The present invention discloses an ultra-high bandwidth photodetector based on a thin-film lithium niobate platform. An epitaxial layer is deposited and grown on a semi-insulating InP substrate. The epitaxial layer sequentially includes a p-type contact layer, an absorption layer, an InGaAsP quaternary layer, a cliff layer, a drift layer and an n-type contact layer. An InP wafer is bonded to a thin-film lithium niobate TFLN to form a configuration with an n region at the bottom and a p region at the top, thereby effectively reducing resistance. The p-type contact layer is a heavily doped InGaAs layer; the n-type contact layer is a heavily doped n-type InP layer. Furthermore, the absorption layer is a 30 nm thick n-doped InGaAs depletion absorption layer and a 110 nm thick graded doping absorption layer. Furthermore, a p-doped InP sacrificial layer is added next to the drift layer. Furthermore, the detector has a 3dB bandwidth of 130GHz and a responsivity of 0.35A / W. An ultra-high bandwidth photodetector based on a thin film lithium niobate platform of the present invention is prepared by the following process: First, 300nm was etched in 600nm thick lithium niobate by dry etching to prepare a low-loss ridge waveguide. Then, the III-V wafer was bonded to the thin-film lithium niobate wafer. The double-mesa structure was prepared by combining dry and wet etching. Finally, the metal electrode was prepared by an electroplating lift-off process. The beneficial technical effects of the present invention are: The photodetector of the present invention exhibits a bandwidth of 130 GHz and a photoelectric responsivity of 0.35 A / W. It is used in an intensity modulated direct detection system and successfully achieves high-quality reception of 50 Gbaud, 60 Gbaud, 80 Gbaud and 100 Gbaud PAM4 signals, with a corresponding maximum signal transmission rate of 200 Gbit / s. The photodetector of the present invention shows potential for application in high-speed, high-capacity communication systems. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 It is the epitaxial layer of the photodetector of the present invention. Figure 2 This is a microscope image of the photodetector of the present invention after double-table etching. Figure 3 This is a microscope image of the photodetector of the present invention. Figure 4 It is the photodetector equivalent circuit model used for S11 fitting and frequency response simulation. Figure 5 Measured and fitted S11 data of the detector (frequency range: 1 GHz to 67 GHz). Figure 6 Measure, fit, and optimize frequency response for detectors. Figure 7 It is the measurement link of IMDD. Figure 8 Eye diagram of PAM4 signal in back-to-back transmission and corresponding bit error rate ((a) 50 Gbaud, (b) 60 Gbaud, (c) 80 Gbaud, (d) 100 Gbaud). DETAILED DESCRIPTION The present invention is further described in detail below with reference to the accompanying drawings and specific implementation methods. The ultra-high bandwidth photodetector based on the thin film lithium niobate platform of the present invention deposits and grows an epitaxial layer on a semi-insulating InP substrate. Figure 1 As shown, it includes p-type contact layer, absorption layer, InGaAsP quaternary layer, cliff layer, drift layer and n-type contact layer in sequence, which helps to alleviate the space charge effect caused by the accumulation of electrons at the InGaAs / InP heterojunction interface. The InP wafer is bonded with the thin film lithium niobate TFLN to form a configuration with the n region at the bottom and the p region at the top, which effectively reduces the resistance and then integrates the photodetector. The p-type contact layer is heavily doped InGaAs to achieve a smaller contact resistance; the n-type contact layer is a heavily doped n-type InP layer. The absorption layer is a 30nm thick n-doped InGaAs depletion absorption layer and a 110nm thick graded doping absorption layer. A p-doped InP sacrificial layer is added next to the drift layer to adjust the electric field within the drift layer to maintain it in the optimal range suitable for electron velocity overshoot. Furthermore, the detector has a 3dB bandwidth of 130GHz and a responsivity of 0.35A / W. An ultra-high bandwidth photodetector based on a thin film lithium niobate platform of the present invention is prepared by the following process: First, 300 nm of the 600 nm thick lithium niobate was etched by dry etching to prepare a low-loss ridge waveguide. Then, the III-V wafer was bonded to the thin-film lithium niobate wafer. The double-table structure was prepared by combining dry and wet etching, such as Figure 2 As shown; finally, the metal electrode is prepared by electroplating lift-off process. Figure 3 Microscope images of the fabricated photodetector are shown. In order to characterize the performance of the detector, the S11 parameter was extracted and an equivalent circuit model was established. The S11 of the detector was measured by a network analyzer with a scanning frequency of up to 67 GHz. By fitting the S11 curve and the equivalent circuit model, the physical parameters of the detector can be extracted. The equivalent circuit model is shown in Figure 4As shown in FIG. 1 , it is composed of a photodetector part, a coplanar waveguide (CPW) part, and an external load resistor. ph represents the current source, C PD and R s represent the photodetector capacitance and series resistance respectively, L CPW and C CPW are the inductance and capacitance of CPW respectively. Figure 5 The measured and fitted S11 values ​​of the detector on the Smith chart are shown. The extracted capacitance and series resistance of the photodetector are 8fF and 25Ω, respectively, and the capacitance and inductance of the CPW are 8.5fF and 30pH, respectively. The bandwidth of the detector is measured by heterodyning. The light from two external cavity lasers is combined to generate an RF signal of different frequencies. The signal is coupled into the device through a lensed fiber with a mode spot size of 2.5μm. A source meter is used to provide the bias voltage and measure the generated photocurrent. The RF signal is extracted through an RF probe (covering DC-67GHz, 75GHz-110 GHz, and 110GHz-170GHz) and a bias tee. An RF power meter records the output power at the corresponding frequency. During the test, the additional loss of the probe, bias tee, and RF power meter has been calibrated. The typical responsivity of the detector at a wavelength of 1550nm is 0.35A / W. The photoelectric frequency response under a -4V bias is as follows Figure 6 The photodetector exhibits a 3-dB bandwidth of up to 130 GHz. The bandwidth can be further improved by carefully designing the coplanar waveguide. When the capacitance and inductance of the CPW reach 17 fF and 90 pH, respectively, the detector bandwidth is expected to exceed 200 GHz, as shown in Figure 2. Figure 6 Shown by the solid line. In order to further verify the performance of the detector in the communication system, the Figure 7 The test link shown detects high-speed PAM4 signals. Figure 7 In the figure: ECL: external cavity laser, PC: polarization controller, AWG: arbitrary waveform generator, MZM: Mach-Zehnder modulator, EDFA: erbium-doped fiber amplifier, VOA: variable optical attenuator, DUT: device under test, RTO: real-time oscilloscope. ) A continuous wave with a wavelength of 1550nm is emitted from the external cavity laser and enters the Mach-Zehnder modulator after passing through the polarization controller. The continuous wave is generated by the arbitrary waveform generator 2 20 The optical signal is then amplified by an erbium-doped fiber amplifier and coupled into the on-chip waveguide via a lensed fiber. The electrical signal generated by the photodetector is extracted by a probe and recorded by a real-time oscilloscope. The received signal is digitally processed to obtain the eye diagram and bit error rate. The detector successfully received and detected PAM4 signals of different baud rates. Figure 5 (ad) shows the back-to-back transmission eye diagrams and bit error rates of 50Gbaud, 60Gbaud, 80Gbaud, and 100Gbaud PAM4 signals. The eye diagrams show that the reception quality is high. The bit error rates of 50Gbaud, 60Gbaud, 80Gbaud, and 100Gbaud PAM4 signals are 4×10 -6 , 6.7×10 -6 , 6×10 -5 and 5.3×10 -4 , which are all lower than the hard decision forward error correction threshold of 3.8×10 -3 The corresponding data rates are 100Gbit / s, 120Gbit / s, 160Gbit / s and 200Gbit / s respectively. In summary, the photodetector of the present invention exhibits a bandwidth of 130 GHz and a photoelectric responsivity of 0.35 A / W. It is used in an intensity modulated direct detection system to successfully achieve high-quality reception of 50 Gbaud, 60 Gbaud, 80 Gbaud and 100 Gbaud PAM4 signals, with a corresponding maximum signal transmission rate of 200 Gbit / s. The photodetector of the present invention shows potential for application in high-speed, high-capacity communication systems.

Claims

1. An ultra-high bandwidth photodetector based on a thin film lithium niobate platform, characterized in that: Deposit and grow epitaxial layers on a semi-insulating InP substrate, the epitaxial layers sequentially include a p-type contact layer, an absorption layer, an InGaAsP quaternary layer, a cliff layer, a drift layer, and an n-type contact layer; bond the InP wafer to a thin film of lithium niobate TFLN to form a configuration with the n region at the bottom and the p region at the top, effectively reducing resistance; The p-type contact layer is a heavily doped InGaAs layer; the n-type contact layer is a heavily doped n-type InP layer.

2. The ultra-high bandwidth photodetector based on a thin film lithium niobate platform according to claim 1, characterized in that: The absorption layer is a 30nm thick n-doped InGaAs depletion absorption layer and a 110nm thick gradient doping absorption layer.

3. The ultra-high bandwidth photodetector based on a thin film lithium niobate platform according to claim 1, characterized in that: A p-doped InP sacrificial layer is added next to the drift layer.

4. The ultra-high bandwidth photodetector based on a thin film lithium niobate platform according to claim 1, characterized in that: The detector has a 3dB bandwidth of 130 GHz and a responsivity of 0.35 A / W.

5. An ultra-high bandwidth photodetector based on a thin film lithium niobate platform according to any one of claims 1 to 4, characterized in that: The detector is prepared by the following process: First, 300nm was etched in 600nm thick lithium niobate by dry etching to prepare a low-loss ridge waveguide. Then, the III-V wafer was bonded to the thin-film lithium niobate wafer. The double-mesa structure was prepared by combining dry and wet etching. Finally, the metal electrode was prepared by an electroplating lift-off process.

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