Heterogeneous integrated coherent receiver based on wafer-level film lithium niobate integrated platform

Abstract

The invention discloses a thin-film lithium niobate coherent receiver based on a wafer-level integration platform. The thin-film lithium niobate coherent receiver is based on an on-chip 2 * 4 90-degree optical mixer and a pair of heterogeneous integrated balanced photoelectric detectors. The 90-degree optical mixer adopts a 2 * 4 MMI coupler based on symmetric interference and a 2 * 2 MMI coupler based on general interference. The balanced photoelectric detector shows a 3dB bandwidth of 60GHz and a common mode rejection ratio greater than 20dB. The large balance detection bandwidth of 60 GHz and the low power consumption of 9.6 fJ / bit are achieved, and data receiving of 512 Gbit / s / Pol in each channel is supported; according to the integrated optical coherent receiver, the characteristics of high bandwidth, ultra-low power consumption and ultra-large capacity of creation records are utilized, and the integrated optical coherent receiver exceeds all other integrated optical coherent receivers shown so far; and a potential way is provided for interconnection of the Pbit / s super-large scale data center in the future.

Description

Technical Field

[0001] The present invention belongs to optical communication technology, and in particular relates to a heterogeneous integrated coherent receiver based on a wafer-level thin-film lithium niobate integrated platform. Background Art

[0002] The growing demand for higher data rates in optical communication systems has driven the exploration and development of advanced technologies capable of supporting terabit-per-second transmissions [1]. The need for high-performance and compact devices is more pressing than ever. Photonic transmitters and receivers are integral components of advanced optical communication systems and must continue to evolve to meet these pressing demands.

[0003] Thin-film lithium niobate (LiNbO3) has emerged as a promising platform for high-performance photonic integrated circuits due to its superior electro-optical properties, wide transparency window, tight mode confinement, and compatibility with high-volume manufacturing processes [2]. State-of-the-art thin-film LiNbO3 I / Q modulators have demonstrated bandwidths exceeding 110 GHz and half-wave voltage (V π ) less than 1V[3]. At the same time, a variety of high-performance lasers[4] and high-speed photodetectors[5] have been realized on the thin-film lithium niobate platform through hybrid and heterogeneous integration technologies. However, despite these advances, the goal of realizing ultra-high-speed coherent receiver chips on thin-film lithium niobate integrated platforms, which are key devices for ultra-large-capacity optical communications, ultra-high-speed photonic computing, and high-performance microwave photonics, has not yet been achieved. This is mainly due to the lack of a reliable wafer-level heterogeneous integration platform. This technical disadvantage greatly limits the application of thin-film integrated chips in these photonic systems.

[0004] References:

[0005] [1] C.

[0006] [2]Z.Li et al., "High density lithium niobate photonic integrated circuits," Nat.Commun., vol.14, no.1, p.4856, 2023.

[0007] [3] M.Xu et al., "Dual-polarization thin-film lithium niobate in-phasequadrature modulators for terabit-per-second transmission," Optica, OPTICA, vol.9, no.1, pp.61–62, Jan.2022, doi:10.1364 / OPTICA.449691.

[0008] [4] CO de Beeck et al., "III / V-on-lithium niobate amplifiers and lasers," Optica, vol.8, no.10, pp.1288–1289, Oct.2021, doi:10.1364 / optica.438620.

[0009]

[15] C. Wei et al., "Ultra-wideband Waveguide-coupled PhotodiodesHeterogeneously Integrated on a Thin-film Lithium Niobate Platform," Light: Advanced Manufacturing, vol.4, no.3, pp.263–271, Dec.2023, doi:10.37188 / lam.2023.030. Summary of the invention

[0010] In view of the above problems, the present invention provides a heterogeneous integrated coherent receiver based on a wafer-level thin-film lithium niobate integration platform.

[0011] The invention discloses a heterogeneous integrated coherent receiver based on a wafer-level thin-film lithium niobate integrated platform, which is based on an on-chip 2×4 90° optical mixer and a pair of heterogeneous integrated balanced photodetectors.

[0012] The 90° optical mixer adopts a 2×4MMI coupler based on symmetric interference and a 2×2MMI coupler based on general interference, wherein the 2×4MMI coupler adopts a wedge structure design and is used to adjust a phase relationship of a pair in the 2×4MMI coupler output pair by 90°.

[0013] Furthermore, before wafer bonding, the wafer-level InP-lithium niobate platform first prepared lithium niobate waveguides and passive devices on the thin-film lithium niobate wafer using an argon dry etching process; after wafer bonding, the InP substrate was selectively corroded using a hydrochloric acid-based solution; next, p-type and n-type mesas were prepared by a chlorine dry etching process to form the main structure of the balanced photodetector; a layer of SiO2 was deposited on the entire wafer surface as a passivation layer; then holes were opened and metal electrodes were formed through electroplating and stripping processes.

[0014] The heterogeneous integrated coherent receiver based on a wafer-level thin-film lithium niobate integrated platform of the present invention has a large balanced detection bandwidth of 60 GHz and low power consumption of 9.6 fJ / bit, and supports data reception of 512 Gbit / s / Pol per channel.

[0015] The beneficial technical effects of the present invention are:

[0016] The coherent receiver of the present invention has a large balanced detection bandwidth of 60 GHz and low power consumption of 9.6 fJ / bit, supports data reception of 512 Gbit / s / Pol per channel, and supports data reception of 7 channels with a total of about 3.6 Tbit / s / Pol. This heterogeneous integrated coherent receiver, with its record-breaking high bandwidth, ultra-low power consumption and ultra-large capacity, surpasses all other integrated optical coherent receivers demonstrated so far, and provides a potential path for future Pbit / s ultra-large-scale data center interconnection. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The fabrication process of heterogeneously integrated coherent receivers on a wafer-level thin-film lithium niobate integration platform.

[0018] Figure 2 It is a wafer-level InP-lithium niobate bonding sheet.

[0019] Figure 3 Colorized microscope image of a wafer-scale thin-film lithium niobate integrated platform waveguide.

[0020] Figure 4 Schematic diagram of a coherent receiver according to the present invention.

[0021] Figure 5 Comparison between the coherent receiver of the present invention and a coin.

[0022] Figure 6 Schematic diagram of a 90° optical mixer.

[0023] Figure 7 is the optical power variation of the simulated 90° mixer.

[0024] Figure 8Figure 2 shows the transmission spectrum of the 90° mixer output in the C-band measured using Mach-Zehnder delay interferometry. Inset: The measured phase deviation of the 90° mixer.

[0025] Fig. 9 is the frequency response of BPD in differential mode and common mode.

[0026] Fig.10 A measurement device for coherent detection.

[0027] Fig.11 Constellation diagrams and corresponding bit error rates for 100 and 128Gbaud QPSK, 80, 100 and 128Gbaud 16QAM, 80 and 100Gbaud 32QAM, and 80 and 100Gbaud 64QAM signals in back-to-back transmission.

[0028] Fig.12 Figure 3 is the relationship between the bit error rate and the received optical power under 100Gbaud QPSK, 100Gbaud 16QAM and 100Gbaud 32QAM signals.

[0029] Fig.13 Constellation diagram and bit error rate for 100Gbaud 16QAM and 100Gbaud QPSK signals transmitted over 25km and 1040km respectively.

[0030] Fig.14 Experimental results of multi-channel communication for a single-chip coherent receiver. DETAILED DESCRIPTION

[0031] The present invention is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0032] The invention discloses a heterogeneous integrated coherent receiver based on a wafer-level thin-film lithium niobate integrated platform, which is based on an on-chip 2×4 90° optical mixer and a pair of heterogeneous integrated balanced photodetectors.

[0033] The main manufacturing process of wafer-level InP-LiNbO3 platform is as follows: Figure 1 Before wafer bonding, lithium niobate waveguides and passive devices are first prepared on thin-film lithium niobate wafers using an argon dry etching process; after wafer bonding, a hydrochloric acid-based solution is used to selectively etch the InP substrate, as shown in FIG. Figure 2 Next, p-type and n-type mesas were prepared by chlorine dry etching to form the main structure of the balanced photodetector; a layer of SiO2 was deposited on the entire wafer surface as a passivation layer; holes were then opened and metal electrodes were formed by electroplating and lift-off processes. Figure 3 A tinted microscope image of the fabricated waveguide is shown.

[0034] The thin-film lithium niobate coherent receiver based on a wafer-level integrated platform of the present invention comprises a 2×4 90° optical mixer and a pair of BPDs (balanced photodiodes), such as Figure 4 After the wafer is cut into 1cm×1cm pieces, as shown in Figure 5 As shown in the figure, the wafer edge is polished to minimize coupling loss. In order to achieve the phase relationship required for coherent detection, the 90° optical mixer uses a 2×4 multimode interference (MMI) coupler based on symmetric interference and a 2×2 MMI coupler based on general interference, as shown in the figure. Figure 6 shown.

[0035] In order to reduce the size of the MMI, the 2×4MMI adopts a wedge-shaped structure design. The 2×2MMI is used to adjust the phase relationship of one pair in the 2×4MMI output pair by 90°. Compared with the traditional 4×4MMI optical mixer, this design avoids the use of crossed waveguides, making the device more compact. Figure 7 The optical simulation of a 90° optical mixer using Lumerical's finite-difference time-domain solver is shown. It can be observed that when light enters the optical mixer from any input port, the optical power is evenly distributed to each output port. A Mach-Zehnder interferometer (MZI) is used to characterize the performance of the 90° optical mixer. Figure 8 The results shown indicate that the phase deviation of the 90° optical mixer is less than ±5° in the spectral range of 1536nm to 1552nm. In addition, optical coherent receivers rely on the performance of balanced photodiodes (BPDs) to capture high-speed electrical signals with the best signal-to-noise ratio. Therefore, the bandwidth and common-mode rejection ratio of the BPDs were tested using the heterodyne method. Fig. 9 The frequency response of the BPD in differential mode and common mode is shown. The BPD exhibits a 3dB bandwidth of 60GHz and a common mode rejection ratio greater than 20dB.

[0036] The coherent receiving system was used to verify the performance of the coherent receiving chip. The experimental setup is as follows: Fig.10As shown. The light emitted by the external cavity laser is divided into two paths: one is modulated by an arbitrary waveform generator (AWG) as signal light; the other is used as local oscillator light. The AWG generates different RF signals to encode the amplitude and phase information of the modulated light in the I and Q channels. These optical signals are then amplified by an erbium-doped fiber amplifier and coupled to the 90° mixer on the chip through equal-length optical fibers with a spot size of 2.5 microns. The four-way output light of the on-chip mixer then enters a balanced detector array, where a bias voltage is applied through a source meter, a bias tee, and a custom GSGSG probe with a frequency range of DC to 67 GHz. The generated RF signal is acquired by a real-time oscilloscope and processed by digital signal processing to recover the original information.

[0037] Fig.11 The constellation diagrams and bit error rates for different signal rates and modulation formats in the back-to-back case are summarized. For the QPSK signal, error-free reception is achieved at a rate of 100 Gbaud (200 Gbit / s), and for a symbol rate of 128 Gbaud (256 Gbit / s), the corresponding bit error rate is 1.7×10 -5 , which is lower than KP4-FEC. The bit error rates of 80Gbaud and 100Gbaud 16QAM signals are 1×10 -3 and 2.3×10 -3 , which are lower than HD-FEC, and the corresponding data rates are 320Gbit / s and 400Gbit / s respectively. Under the condition that the bit error rate is lower than SD-FEC, 128Gbaud 16QAM (bit error rate = 3.4×10 -2 ), 80Gbaud32QAM (bit error rate = 1.1×10 -2 ), 100Gbaud 32QAM (BER=2.6×10 -2 ) and 80Gbaud64QAM (BER=3.1×10 -2 ) signals can be successfully received, corresponding to a maximum data rate of 512Gbit / s. In addition, for 100Gbaud 64QAM (600Gbit / s) signals, the bit error rate is less than 0.05, and when using 28% FEC coding, the bit error rate can reach 10 -6 Below. Fig.12As shown, the relationship between the back-to-back bit error rate and the received optical power was tested for 100Gbaud QPSK, 100Gbaud 16QAM and 100Gbaud 32QAM signals. For the 100Gbaud QPSK signal, when the received optical power was -2dBm, 0dBm and 2dBm, the measured transmission rate was lower than SD-FEC, HD-FEC and KP-FEC, respectively. For the 100Gbaud 16QAM and 100Gbaud 32QAM signals, when the incident power reached 1dBm and 6dBm, respectively, the received bit error rate was lower than SD-FEC. In addition, we also conducted long-distance transmission communication experiments using coherent receivers. The experimental results are shown in Fig.13 After 25 km of single-mode fiber transmission, the bit error rate of the received 100Gbaud 16QAM signal is 3.9×10 -2 For a 100Gbaud QPSK signal, the bit error rate after 1040km transmission is 2.2×10 -2 In the experimental setup, optical amplification (16dB gain) was performed every 80 km of optical fiber transmission (~16dB loss). Finally, a back-to-back multi-channel communication experiment was conducted on the coherent receiving chip. The results are shown in Figure 2. Fig.14 As shown. When the threshold is 4×10 -2 In this case, 7 channels of 128Gbaud 16QAM signals were successfully received, bringing the total communication capacity of the single chip to nearly 3.6Tbps.

[0038] The present invention demonstrates for the first time a high-speed thin-film lithium niobate coherent receiver chip, the first such chip implemented on the developed InP-LiNbO3 wafer-level integration platform, which combines the advantages of InP and LiNbO3. The thin-film lithium niobate optical coherent receiver has a large balanced detection bandwidth of 60GHz and a common mode rejection ratio (CMRR) greater than 20dB. The single-polarization I / Q coherent receiver combines a compact 2×4 90° optical mixer and a balanced photodiode (BPD) array to achieve a receiving capacity record of 512Gbit / s / λ under a 128Gbaud 16th-order quadrature amplitude modulation (QAM) signal. In addition, the long-distance reception capability of receiving 100Gbaud quadrature phase-shift keying (QPSK) signals over a transmission distance of 1040 kilometers has been demonstrated. The work of the present invention shows the potential for Pbit / s-level applications of this technology in future ultra-large-scale data center interconnections.

Claims

1. A heterogeneous integrated coherent receiver based on a wafer-level thin-film lithium niobate integrated platform, characterized in that: The coherent receiver combines a compact 2×4 90° optical mixer and a balanced photodetector array; The 90° optical mixer adopts a 2×4 MMI coupler based on symmetric interference and a 2×2 MMI coupler based on general interference.

2. A heterogeneous integrated coherent receiver based on a wafer-level thin-film lithium niobate integrated platform according to claim 1, characterized in that: The wafer-level InP-lithium niobate platform first prepares lithium niobate waveguides and passive devices on thin-film lithium niobate wafers using an argon dry etching process before wafer bonding; after wafer bonding, the InP substrate is selectively etched using a hydrochloric acid-based solution; next, p-type and n-type mesas are prepared by a chlorine dry etching process to form the main structure of the balanced photodetector; a layer of SiO2 is deposited on the entire wafer surface as a passivation layer; Holes are then opened and metal electrodes are formed through electroplating and lift-off processes.

3. The heterogeneous integrated coherent receiver based on a wafer-level thin-film lithium niobate integrated platform according to claim 1, characterized in that: The 2×4 MMI coupler adopts a wedge-shaped structure design.

4. The heterogeneous integrated coherent receiver based on a wafer-level thin-film lithium niobate integrated platform according to claim 1, characterized in that: The 2×2 MMI coupler is used to adjust the phase relationship of one pair of output pairs of the 2×4 MMI coupler by 90°.

5. A heterogeneous integrated coherent receiver based on a wafer-level thin-film lithium niobate integrated platform according to any one of claims 1 to 4, characterized in that: The coherent receiver has a large balanced detection bandwidth of 60 GHz and low power consumption of 9.6 fJ / bit, and supports data reception of 512 Gbit / s / Pol per channel.

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