Thin film lithium niobate heterogeneous integrated high-performance balanced photoelectric detector

Abstract

The invention discloses a thin-film lithium niobate heterogeneous integrated high-performance balanced photoelectric detector, which is characterized in that an III-V wafer and a thin-film lithium niobate wafer are bonded together by using a wafer bonding technology, and an III-V epitaxial structure is formed by growing through metal organic chemical vapor deposition; the device sequentially comprises a p-type contact layer, an InGaAs absorption layer, a quaternary layer, a cliff layer, a drift layer, an InP sacrificial layer and an n-type contact layer. The balanced photoelectric detector disclosed by the invention shows a high bandwidth of 55GHz and a common-mode rejection ratio greater than 10dB; the method is applied to a coherent detection system, and error-free transmission of 50GBad and 100GBad quadrature phase shift keying signals and high-quality receiving of 80GBad and 100GBad 16-order quadrature amplitude modulation signals are realized.

Description

Technical Field

[0001] The present invention belongs to the field of photoelectric detection technology, and in particular relates to a thin-film lithium niobate heterogeneous integrated high-performance balanced photoelectric detector. Background Art

[0002] Coherent optical communications using advanced modulation formats provide a reliable solution for high-speed, high-capacity, and long-distance transmission communication networks [1]. Balanced photodiodes (BPDs) have been widely studied as key devices in coherent optical communications [2], [3]. With the increasing demand for low power consumption and large-scale systems, the miniaturization and integration of devices has become a trend. Integrated photonics has significant advantages such as large bandwidth, strong scalability, and miniaturization, which has promoted the development of high-speed, high-capacity, and low-cost optical communication systems [4]. In the past decade, on-chip balanced photodetectors have been successfully implemented on silicon-based, aluminum nitride [5], and silicon nitride [6] integrated platforms, showing excellent performance. The thin-film lithium niobate (TFLN) platform has become a strong candidate platform for integrated photonics due to its excellent optoelectronic properties, but so far only single photodiodes (SPDs) have been realized [7], [8]. Recently, a broadband single photodetector heterogeneously integrated on TFLN by wafer bonding achieved 80 GHz bandwidth and 0.6 A / W responsivity [7]. In our previous work, we also reported a high-speed single photodetector with 110 GHz bandwidth and 0.4 A / W responsivity [8]. The development of balanced photodetectors on the TFLN platform is still an urgent need.

[0003] References:

[0004] [1]Y.Wang et al., "Ultrahigh-speed graphene-based optical coherent receiver," Nat Commun, vol.12, no.1, p.5076, Aug.2021, doi:10.1038 / s41467-021-25374-0.

[0005] [2]P.Runge et al.,“Waveguide Integrated Balanced Photodetectors forCoherent Receivers,”IEEE J.Select.Topics Quantum Electron.,vol.24,no.2,pp.1–7,Mar.2018,doi:10.1109 / JSTQE.2017.2723844.

[0006] [3]R.Costanzo,Z.Yang,A.Beling,and S.M.Bowers,“Wideband BalancedPhotoreceivers With InP-Based Photodiodes and 65nm CMOS TIAs for Use inOptical Frequency Synthesis Systems,”J.Lightwave Technol.,vol.37,no.23,pp.5833–5839,Dec.2019,doi:10.1109 / JLT.2019.2940208.

[0007] [4]D.Zhu et al.,“Integrated photonics on thin-film lithium niobate,”Adv.Opt.Photon.,vol.13,no.2,p.242,Jun.2021,doi:10.1364 / AOP.411024.

[0008] [5]X.Xie et al.,“High-Power and High-Speed Heterogeneously IntegratedWaveguide-Coupled Photodiodes on Silicon-on-Insulator,”J.Lightwave Technol.,vol.34,no.1,pp.73–78,Jan.2016,doi:10.1109 / JLT.2015.2491258.

[0009] [6] J.Gao et al., "Heterogeneous balanced photodetector on siliconnitride with 30GHz bandwidth and 26dB common mode rejection ratio," in 2023 Optical Fiber Communications Conference and Exhibition (OFC), San Diego, CA, USA: IEEE, Mar. 2023, pp.1–3.doi:10.23919 / OFC49934.2023.10116763.

[0010] [7]X.Guo et al., "High-performance modified uni-traveling carrierphotodiode integrated on athin-film lithium niobate platform," Photon.Res., vol.10, no.6, p.1338, Jun.2022, doi:10.1364 / PRJ.455969.

[0011] [8] C. Wei et al., "Ultra-wideband Waveguide-coupled PhotodiodesHeterogeneously Integrated on a Thin-film Lithium Niobate Platform," Light: Advanced Manufacturing, vol.4, no.3, p.1, 2023, doi:10.37188 / lam.2023.030. Summary of the invention

[0012] In view of the above situation, the present invention provides a thin-film lithium niobate heterogeneous integrated high-performance balanced photodetector.

[0013] The invention discloses a thin-film lithium niobate heterogeneous integrated high-performance balanced photodetector. A III-V wafer and a TFLN wafer are bonded together by wafer bonding technology. The III-V epitaxial structure is grown by metal organic chemical vapor deposition and sequentially comprises a p-type contact layer, an InGaAs absorption layer, a quaternary layer, a cliff layer, a drift layer, an InP sacrificial layer and an n-type contact layer.

[0014] Furthermore, the total thickness of the InGaAs absorption layer is 140 nm, including a 110 nm gradient doping absorption layer and a 30 nm depletion absorption layer.

[0015] Furthermore, the drift layer thickness is 120 nm to minimize the transit time.

[0016] Furthermore, the InP sacrificial layer is used to adjust the electric field in the drift layer and utilize the overshoot effect.

[0017] Furthermore, the balanced photodetector has a high bandwidth of 55 GHz and a common-mode rejection ratio greater than 10 dB.

[0018] The invention discloses an application of a thin-film lithium niobate heterogeneously integrated high-performance balanced photodetector: a pair of balanced photodetectors is combined with a commercial 90° mixer to form a high-speed coherent receiver for coherent optical communication experiments.

[0019] The beneficial technical effects of the present invention compared with the prior art are:

[0020] The balanced photodetector of the present invention exhibits a high bandwidth of 55 GHz and a common-mode rejection ratio (CMRR) greater than 10 dB. The device has been applied to coherent detection systems, achieving error-free transmission of 50 Gbaud and 100 Gbaud quadrature phase shift keying (QPSK) signals, as well as high-quality reception of 80 Gbaud and 100 Gbaud 16th-order quadrature amplitude modulation (QAM) signals. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a microscope image of the photodetector electrode of the present invention before deposition.

[0022] Figure 2 This is a microscope image of the photodetector electrode after deposition of the present invention.

[0023] Figure 3 Experimental setup for frequency response measurements.

[0024] Figure 4 The photoelectric frequency response of the balanced photodetector of the present invention is achieved.

[0025] Figure 5 Experimental verification of coherent detection.

[0026] Figure 6The constellation diagram of the 16QAM signal and the corresponding bit error rate ((a) 50 Gbaud and (b) 100 Gbaud QPSK, (c) 80 Gbaud and (d) 100 Gbaud) of Example 1. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0028] The invention discloses a thin-film lithium niobate heterogeneous integrated high-performance balanced photodetector. A III-V wafer is bonded to a TFLN wafer by using wafer bonding technology. Its III-V epitaxial structure is grown by metal organic chemical vapor deposition and sequentially includes a p-type contact layer, an InGaAs absorption layer, a quaternary layer, a cliff layer, a drift layer, an InP sacrificial layer and an n-type contact layer.

[0029] The total thickness of the InGaAs absorption layer is 140nm, including 110nm of gradient doping absorption layer and 30nm of depletion absorption layer. The gradient doping profile is used to form a built-in electric field, thereby accelerating the diffusion of photogenerated electrons.

[0030] The drift layer thickness is 120 nm to minimize the transit time.

[0031] The InP sacrificial layer is used to adjust the electric field in the drift layer and utilize the overshoot effect.

[0032] The manufacturing process of the balanced photodetector is as follows:

[0033] Lithium niobate waveguides were prepared by dry etching; III-V wafers were bonded to TFLN wafers using wafer bonding technology; active area structures were prepared by dry and wet etching; and finally, metal electrodes were prepared by electroplating stripping. Figure 1 and Figure 2 Figure 2 shows microscope images of the device before and after electrode fabrication.

[0034] like Figure 3 The test chain shown is used to characterize the frequency response of a balanced photodetector ( Figure 3In: ECL: external cavity laser, PC: polarization controller, EDFA: erbium-doped fiber amplifier, VODL: variable optical delay line, VOA: variable optical attenuator, RF power: RF power meter). The optical beat signal is generated by two external cavity lasers and amplified by the erbium-doped fiber amplifier before being divided into two channels. The phase difference and power of the two branches are controlled by the adjustable optical delay line and the adjustable optical attenuator respectively. The common mode and differential mode conversion between the two channels is achieved by adjusting the delay line. The optical attenuator ensures the consistency of the power of the two signals, making the measurement of bandwidth and common mode rejection ratio more accurate. The optical signal is coupled to the waveguide on the chip through a lensed fiber with a spot size of 2.5μm and enters the BPD for detection. The generated electrical signal is extracted by a signal-ground-signal (SGS) probe and input into the power meter for recording. Additional RF losses have been calibrated.

[0035] Figure 4 The frequency response of the device in differential mode and common mode is shown. The diamond represents the frequency response in differential mode, the dotted line represents the fitted frequency response in differential mode, and the triangle represents the frequency response in common mode. It can be seen that the balanced photodetector has a 3dB bandwidth of 55GHz. In the frequency range of DC to 67GHz, the common-mode rejection ratio of the balanced photodetector is greater than 10dB.

[0036] like Figure 5 As shown, a pair of balanced photodetectors combined with a commercial 90° mixer formed a high-speed coherent receiver for coherent optical communication experiments to evaluate the performance of the fabricated BPD. Figure 5 In the figure, AWG: arbitrary waveform generator, IQM: I / Q modulator, RTO: real-time oscilloscope. The continuous wave emitted by the laser is divided into two paths: one is used as signal light to load the RF signal, and the other is used as local oscillator light. The signal light is introduced into the I / Q modulator, where it is modulated by the RF signal generated by the arbitrary waveform generator. The RF signal adopts QPSK and 16QAM modulation formats respectively. The modulated signal light and local oscillator light are amplified and coherently combined in the 90° mixer. The optical signal is introduced into the BPD on the chip through the lens fiber for coherent detection. Similar to the bandwidth test, the received RF signal is extracted by the SGS probe and input into the real-time oscilloscope. After digital signal processing, the constellation diagram of the signal is obtained. In addition, the corresponding bit error rates (BER) are calculated by mapping symbols to bits.

[0037] The above coherent receiving system successfully achieved error-free transmission of QPSK signals with 50Gbaud and 100Gbaud symbol rates. Figure 6(a) and (b) show the measured constellation diagrams of 50Gbaud and 100Gbaud QPSK signals, respectively. The balanced photodetector also successfully received high-quality 16QAM signals at 80Gbaud and 100Gbaud, such as Figure 6 (c) and (d). The bit error rate of the 80Gbaud16QAM signal is 1.2×10-3, which is lower than the hard decision forward error correction threshold (3.8×10-3). The bit error rate of the 100Gbaud 16QAM signal is 1×10-2, which is lower than the 20% soft decision forward error correction threshold (2.4×10-2). It is worth noting that the 30GHz bandwidth of the modulator limits the system performance, and the balanced photodetector shows the potential to receive higher rate signals. In addition, the generated RF signal does not pass through any RF amplification device, which significantly reduces the power consumption of the system and prevents further deterioration of the signal-to-noise ratio.

[0038] In summary, the present invention proposes and experimentally verifies a waveguide-coupled modified uni-traveling carrier (MUTC) balanced photodetector heterogeneously integrated on a thin-film lithium niobate platform. The balanced photodetector exhibits a 3dB bandwidth of 55GHz and a common-mode rejection ratio greater than 10dB. In addition, the balanced photodetector achieves high-quality detection of signals with a maximum rate of 400Gbit / s (100Gbaud 16QAM) without the need for a series RF amplifier, demonstrating its potential in high-speed, high-capacity, low-power coherent communication systems.

Claims

1. A thin-film lithium niobate heterogeneous integrated high-performance balanced photodetector, characterized in that: The III-V wafer is bonded to the TFLN wafer using wafer bonding technology. Its III-V epitaxial structure is grown by metal organic chemical vapor deposition, which includes p-type contact layer, InGaAs absorption layer, quaternary layer, cliff layer, drift layer, InP sacrificial layer and n-type contact layer in sequence.

2. The thin-film lithium niobate heterogeneous integrated high-performance balanced photodetector according to claim 1, characterized in that: The total thickness of the InGaAs absorption layer is 140 nm, including a 110 nm gradient doping absorption layer and a 30 nm depletion absorption layer.

3. The thin-film lithium niobate heterogeneous integrated high-performance balanced photodetector according to claim 1, characterized in that: The drift layer thickness is 120 nm to minimize the transit time.

4. The thin-film lithium niobate heterogeneous integrated high-performance balanced photodetector according to claim 1, characterized in that: The InP sacrificial layer is used to adjust the electric field in the drift layer and utilize the electron velocity overshoot effect.

5. The thin-film lithium niobate heterogeneous integrated high-performance balanced photodetector according to claim 1, characterized in that: The balanced photodetector has a high bandwidth of 55 GHz and a common mode rejection ratio greater than 10 dB.

6. A thin-film lithium niobate heterogeneous integrated high-performance balanced photodetector according to any one of claims 1 to 5, characterized in that: A pair of balanced photodetectors combined with a commercial 90° mixer forms a high-speed coherent receiver for coherent optical communication experiments.

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