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Abstract
We demonstrate a Ge electro-absorption modulator (EAM) in L band with a 3 dB electro-optical bandwidth beyond 67 GHz at −3 V bias voltage. The Eye diagram measurement shows a data rate of over 80 Gbps for non-return-to-zero on-off keying (NRZ-OOK) modulation at a voltage swing of 2.3 Vpp and the wavelength of 1605 nm. Through the comparison of multi-device results, it is proved that the introduction of the annealing process after CMP can increase the mean static extinction ratio of the EAM from 7.27 dB to 11.83 dB, which confirms the manufacturability of the device. The dynamic power consumption of the device is 6.348 fJ/bit. The performance of our device is comprehensive. The Ge EAM device also has excellent performance as a photodetector (PD) in the C and L communication bands. The responsivity of the device is 1.04 A/W at the wavelength of 1610 nm, resulting in ∼0.87 mW of static power consumption at −3 V bias voltage under 0.28 mW of optical input and the 3 dB opto-electric bandwidth of the devices are beyond 43 GHz at −3 V bias.
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1. Introduction
With the increasing demand for data transmission, information congestion caused by the bandwidth and energy consumption problems of traditional electrical interconnections is becoming more and more serious. The optical interconnect is becoming the most promising solution due to its advantages of large bandwidth, strong anti-crosstalk capability and low energy consumption [1]. Particularly, silicon photonics enables hybrid integration of optoelectronics, which is CMOS compatible with the advantages of high integration density and low cost [2]. Since 1980s, silicon photonics devices including directional couplers (DC) [3,4], grating couplers [5,6], multimode interferometers (MMI) [7,8], photodetectors [9–12] and modulators [13–15] have been extensively studied.
Modulators are often considered an essential device of the on-chip interconnect. At present, the Mach-Zehnder interferometer (MZI) modulator based on the plasma dispersion effect is the most widely used. Its advantages are large optical bandwidth, high extinction ratio and high modulation rate [16–19]. There has been a MZI modulator with a non-return-to-zero (NRZ) modulation rate of 60 Gbps [20]. Generally, the MZI modulator suffers from the large footprint and complex structure design of travelling wave electrodes, which has a high energy consumption. Unlike the MZI, the micro-ring modulator has a small physical footprint and low energy consumption, but based on the resonance principle the optical bandwidth is extremely low and the performance is easily affected by the process variation and operating temperature [21–23]. Ge or GeSi electro-absorption modulator (EAM) based on the Franz-Keldysh (FK) effect has also been a potential solution for the modulators, with the advantages of the small footprint, reasonable optical bandwidth, high extinction ratio, lumped electrodes design and high modulation rate [24–26].
There were many works on the EAM based on the FK effect. Liu J et al. first demonstrated a vertical GeSi EAM with the area of only 30 µm2 and the energy consumption of 50 fJ/bit in the C band [27]. Afterwards, DZ. Feng et al. fabricated a GeSi EAM with horizontal p-i-n structure on a six inch SOI wafers with 0.4 µm thick buried oxide (BOX) and a 3 µm thick silicon epitaxial layer, whose width of GeSi was 10 µm. This p-i-n configuration enabled a very narrow intrinsic GeSi region, hence reducing the voltage swing required to achieve a high extinction ratio of 6 dB. However, the GeSi was under-etched, leaving a GeSi slab thickness of around 0.55 µm causing excess transition loss between the silicon waveguide and the GeSi waveguide. The optical bandwidth exceeded 35 nm and the 3 dB bandwidth was 40.7 GHz in the wavelength band of 1550 nm. [28] Subsequently, S. A. Srinivasan et al. exhibited a Ge EAM with a width of 0.6 µm on a standard 220 nm SOI platform at IMEC, Belgium. The GeSi material was selectively grown in a recessed Si region. High temperature anneal was applied to the wafer to reduce the treading dislocation density and afterwards, the over-grown GeSi was planarized by chemical mechanical polishing. The modulators were fabricated in imec’s silicon photonics platform with other passive and active components with the extinction ratio of 3.3 dB and the data rate of 56 Gb/s by applying a voltage swing of 2 Vpp at the wavelength of 1610 nm. [29] Zhi Liu et al. also demonstrated a wrap-around PIN Si/GeSi EAM with dimensions of 1.5 µm x 40 µm developed on an 800 nm thick SOI platform. The advantage of the structure was provided by the wrap-around diode structure enabling a better control of the junction width whilst alleviating the constraint linked to the width of the waveguide. The 3 dB bandwidth was 36 GHz at −1 V bias voltage and the data rate was 56 Gbps at a voltage swing of 3 Vpp. [30] The EAM device based on the FK effect can be further improved in terms of bandwidth and data rate by optimizing the structure design and implantation conditions. In addition, the EAM has been applied to I/Q modulators, which is in a differentially driven MZ interferometric configuration similar to the MZM based I/Q modulators, whose symbol rate is up to 100 Gbaud with single-polarization QAM signal generation. [31] This also broadens the application scenarios of the EAM in the field of coherent optical communication, laying a foundation for the wide application of the EAM.
In this paper, we present a horizontal Ge EAM with a width of ∼600 nm and a length of 40 µm on a 220 nm SOI silicon photonics platform. A high temperature anneal (850°C 3 min in H2) is performed after Ge CMP to reduce surface defects caused by the CMP process to improve the extinction ratio (ER) of the device. And the high-frequency performance of the device can be improved by adjusting the doping concentration. The Ge EAM has an insertion loss (IL) of 5.73 dB and a static extinction ratio of 14.15 dB at −3 V bias voltage and the wavelength of 1603 nm, and the manufacturability is demonstrated by multi-device comparison. The device has a 3 dB electro-optical bandwidth beyond 67 GHz at −3 V bias voltage. Clear open eye diagrams are demonstrated at an NRZ data rate over 80 Gbps at a voltage swing of 2.3 Vpp. The dynamic power consumption of the device is 6.348 fJ/bit. The same design of the Ge EAM can also work as a photodetector. The dark current is about 0.12 µA at −3 V, and the responsivity is 1.04 A/W at the wavelength of 1610 nm with ∼0.87 mW of static power consumption under 0.28 mW of optical input at −3 V bias voltage. The devices show high 3 dB opto-electric bandwidths beyond 43 GHz at −3 V bias voltage.
2. Device design and fabrication
Figure 1 shows a schematic structure of the EAM device. The device was fabricated at the Shanghai Industrial µTechnology Research Institute (SITRI) using the 8-inch silicon photonics platform. Ge waveguide has a length of 40 µm and a width of 600 nm. The Ge waveguide is based on a horizontal PIN junction. The main fabrication steps are shown in Fig. 2. The device starts on an SOI substrate with a 220-nm-thick Si top layer and a 2-µm-thick buried oxide. First, the top silicon is etched to form a 150nm thick rib waveguide and a 220 nm thick strip waveguide, respectively. Then p-Si, n-Si, p++-Si and n++-Si doping are performed using the ion implantations in silicon. Afterwards, a 110 nm-deep Si is etched into the rib waveguide, where the Ge waveguide is then epitaxially grown by reduced pressure chemical vapor deposition (RPCVD), and polished by chemical mechanical polishing (CMP). A high temperature anneal is performed to reduce the surface defects induced by the CMP process. Next Ge is doped with boron and phosphorous at a concentration of ∼7e16 cm−3 respectively followed a rapid thermal anneal. Finally the SiO2 layer is covered and the electrodes are manufactured.
Fig. 2. The main fabrication steps of the horizontal Ge EAM. (a) etching to form a rib structure; (b) doping of the silicon; (c) etching 110 nm Si; (d) epitaxial growth of the germanium waveguide, CMP and high temperature anneal after Ge CMP; (e) Doping of the Ge waveguide; (f) SiO2 covering and electrodes fabrication.
Figure 3 shows a cross-sectional view of the Scanning Electron Microscope (SEM) of the device and an enlarged diagram of a transmission electron microscope (TEM) of the waveguide. The Ge waveguide has a height of 350.9 nm and a width of 622.2 nm. As a result of the high temperature annealing, the Ge atoms diffuse to a certain extent on the surface of the waveguide. Therefore the flat surface after CMP becomes rounded.
3. Measurement results
3.1 Modulator measurement
The performance of the EAM is first measured using the setup illustrated in Fig. 4 with the Keysight 8164B Lightwave measurement system (81606A tunable laser source and 81635A optical power sensor), Thorlabs FPC561 fiber polarization controller, DC probe and Keysight 2450 source meter. Figure 5(a) shows the optical transmission loss (including coupling loss) of the device and reference waveguide from 0 V to −3 V bias voltage. Since the optimal operating wavelength of the grating coupler is 1550 nm, the coupling loss of a single grating coupler at the wavelength of 1610 nm is about 6.27 dB. After subtracting the loss of the reference waveguide respectively, the insertion loss of the device and the extinction ratio from −1 V to −3 V are obtained, as shown in Fig. 5(b). The insertion loss of the EAM is about 6.4 dB at the wavelength of 1610 nm. The coupling loss between the Si waveguide and the Ge waveguide is calculated to be 0.53 dB per side. The overall coupling loss is then 1.06 dB. To assess the EAM performance in the L band, we use a figure of merit (FOM = ER/IL). As shown in Fig. 5(c), the maximum FOM of the EAM is 1.18 near the wavelength of 1610 nm at −2 V bias voltage, and the maximum FOM of the EAM at −3 V bias voltage is 2.47 where the ER is 14.15 dB near the wavelength of 1613 nm. Figure 5(d) shows the insertion loss and extinction ratio extracted from 5 devices without annealing. The ER at −3 V bias voltage has a mean value of 7.27 dB with a standard deviation of 1.43 dB. The insertion loss has an average value of 8.5 dB with a standard deviation of 3.5 dB. In comparison, Fig. 5(e) shows the performance extracted from 10 devices with annealing after CMP. The ER at −3 V bias voltage has an average value of 11.83 dB with a standard deviation of 2.3 dB. The insertion loss has an average value of 6.33 dB with a standard deviation of 1.67 dB. The Ge atoms diffuse during the annealing process which causes an arc shape of the top surface. Surface defects can also be reduced after the high temperature anneal. However, the standard deviation values of the devices are high due to the poor uniformity of Ge CMP. It can still prove that our devices have excellent performance of high ER and FOM.
Fig. 5. (a) Loss spectra of the EAM under different bias voltages; (b) insertion loss and extinction ratios of the EAM under different bias voltages; (c) FOM of the EAM under different bias voltages; (d) IL and ER at 1610 nm across 5 devices without annealing; (e) IL and ER at 1610 nm across 10 devices with annealing.
The 3 dB bandwidth and eye diagram of the EAM were tested on the high frequency platform at the National Information Optoelectronics Innovation Center. The test was conducted at 1605 nm where the minimum insertion loss was found. As shown in Fig. 6(a), the 3 dB electro-optical bandwidth of the EAM exceeds 67 GHz at −3 V bias, and can only be tested to 67 GHz due to the limitation of the equipment. Because the FK effect was a sub-picosecond phenomenon, the speed of the FK modulator is only limited by the resistor capacitor (RC) delay [32]. An equivalent circuit model (the inset in Fig. 6(b)) is used for extracting the electrical parameters of the device. In the equivalent circuit model, Cm is the capacitance of the pads, Cj is the junction capacitance, Rs is the series resistance, Cox is the capacitance of the BOX layer, and Rsi is the resistance of the substrate. On fitting the model to the S11 parameter across the device, the extracted junction capacitance of the modulator is estimated to be 4.8 fF, along with a series resistance of 250 Ω suggesting a RC limited bandwidth beyond 130 GHz.
Fig. 6. (a) 3 dB electro-optical bandwidth of the EAM; (b)imag and (c) real S11 curves of the EAM at −3 V. The inset is the equivalent circuit model of the EAM with extracted resistances and capacitances.
Eye diagrams are measured to explore the high-speed performance of the EAM. 40 Gbps, 53 Gbps, 72 Gbps and 80 Gbps (29−1) NRZ pseudorandom binary sequence (PRBS) electrical signals are generated by a bit pattern generator. These electrical signals are amplified by an RF amplifier to the peak-to-peak voltage (Vpp) of 2.3 V, which is applied to the device via a bias T and a 50 Ω-terminated GS RF probe. The bias voltage, which adjusts the operating condition of the EAM, is −3 V. As shown in Fig. 7, the eye diagram of the EAM is still clear when the modulation rate is 80 Gbps, and the eye opening is still obvious, indicating that the maximum modulation rate of the EAM is beyond 80 Gbps.
The dynamic power consumption per bit could be estimated by (CjVpp2)/4 [34]. The Cj and the Vpp of the EAM are ∼4.8 Ff and 2.3 V, respectively. Thus, the dynamic power consumption of the device is 6.348 fJ/bit. For comparisons, performance of the reported Ge or GeSi EAMs is shown in Table 1 [28–30,33–35]. Our device has a higher static extinction ratio and thus higher FOM. The doping of the Ge waveguide enhances the electric field strength, while the Ge waveguide structure with a high middle and low sides, as shown in Fig. 3, makes the optical field more have a better overlap with the electric field. The annealing process after CMP reduces the defects on the Ge surface and enables the rearrangement of Ge atoms to further improve the device performance. In addition, our device has a higher bandwidth beyond 67 GHz and a higher data rate beyond 80 Gbps. Moreover, the high-frequency performance of the device is limited by the test, and thus we believe the actual bandwidth and data rate will far exceed the current results.
Table 1. EAM in literature compared to our device.
3.2 Detector measurement
The opto-electronic properties of this device are characterized as a Ge photodetector. The setup diagram is shown in Fig. 8. Figure 9 shows the I-V characteristics of the device with and without illumination. The dark current of the device is 0.12 µA at −3 V, larger than the reported similar device whose dark current is around 10 nA [35]. This may be due to defects at the Ge/Si interface and defects after Ge CMP. By adjusting the angle of the incident fiber, the opto-electric tests are carried out at the wavelength of 1610 nm, respectively. At the wavelength of 1610 nm, the actual incident optical power into the waveguide is 0.28 mW and the light current is 0.29 mA at −3 V. Thus, the responsivity is 1.04 A/W. The static power consumption of the device can be estimated as mean current multiplied by DC bias voltage, which is about 0.87 mW at −3 V under 0.28 mW of optical input.
The opto-electric bandwidth of this device was measured with the Keysight N5227B 67 GHz network analyzer and Lightwave component analyzer (LCA). The RF system was calibrated to normalize the measurement with the RF response of the Cascade infinity GS probe, cables, SHF bias T and Keysight 2450 source meter shown in Fig. 8(b). Figure 10 shows the opto-electric response (S21) of the device at −3 V bias voltage. The 3 dB opto-electric bandwidth of the device is 50.4 GHz at the waveguide of 1610 nm, and the illustration shows that the bandwidth across 5 devices are all beyond 43 GHz. Combined with the responsivity mentioned above, the device has the potential to be used as a photodetector. Compared with the typically used Ge photodetector, it has the disadvantages of the relatively large footprint and high dark current.
For comparison, performance of the reported Ge PDs is shown in Table 2 [36–38]. The responsivity and 3 dB opto-electric bandwidth of the device are high. The device has the potential to be used as a photodetector, but is only slightly larger in size and slightly higher in dark current than the conventional photodetectors.
Table 2. PD in literature compared to our device.
4. Conclusion
A horizontal Ge waveguide EAM is demonstrated. Through the comparison of multi-device results, it is proved that the introduction of the annealing process after CMP can increase the mean ER of the EAM from 7.27 dB to 11.83 dB. The FOM of the EAM can reach 2.47 at −3 V bias voltage and the wavelength of 1603 nm. The 3 dB electro-optical bandwidth exceeds 67 GHz at −3 V bias voltage, and the maximum modulation rate for NRZ signal is beyond 80 Gbps at a swing of 2.3 Vpp. The dynamic power consumption of the device is 6.348 fJ/bit. In addition, the responsivity of the device is 1.04 A/W at the wavelength of 1610 nm, resulting in ∼0.87 mW static power consumption under 0.28 mW of optical input at −3 V bias voltage. The devices show high 3 dB opto-electric bandwidths beyond 43 GHz at the wavelength of 1610 nm. The EAM exhibits a relatively high insertion loss, which can be further improved by reducing the length of the Ge waveguide and optimizing the coupling between Si waveguide and Ge waveguide. The on-chip DC bias can also be added to reduce the impact of an external bias T during the high-frequency performance testing. The current operation wavelength of 1610 nm can be shifted to 1550 nm with the incorporation of ∼0.8% Si during Ge epitaxial growth [28]. Overall, we demonstrate a horizontal Ge device working both as a EAM and a PD with the good performance, which also provides a new idea for silicon photonics co-integration.
Funding
National Outstanding Youth Foundation of China (61904185); Strategic Pioneer Research Projects of Defense Science and Technology (XDB43020500); Key project of National Natural Science Foundation of China (61935003); Shanghai Sailing Program (20YF1456900).
Disclosures
The authors declare no conflict of interests.
Data availability
Data underlying the results presented in this work are not publicly available at this moment but may be obtained from the authors upon reasonable request.
References
1. T. Yatagai, S. Kawai, and H. Huang, “Optical computing and interconnects,” Proc. IEEE 84(6), 828–852 (1996). [CrossRef]
2. Y. Liu, S. Wang, J. Wang, X. Li, M. Yu, and Y. Cai, “Silicon photonic transceivers in the field of optical communication,” Nano Communication Networks 31, 100379 (2022). [CrossRef]
3. B. Jalali, P. D. Trinh, S. Yegnanarayanan, and F. Coppinger, “Guided-wave optics in silicon-on-insulator technology,” IEE Proceedings-optoelectronics 143(5), 307–311 (1996). [CrossRef]
4. D. Dai and S. Wang, “Asymmetric directional couplers based on silicon nanophotonic waveguides and applications,” Front. Optoelectron. 9(3), 450–465 (2016). [CrossRef]
5. D. Taillaert, W. Bogaerts, P. Bienstman, T.F. Krauss, P. Van Daele, I. Moerman, S. Verstuyft, K. De Mesel, and R. Baets, “An out-of-plane grating coupler for efficient butt-coupling between compact planar waveguides and single-mode fibers,” IEEE J. Quantum Electron. 38(7), 949–955 (2002). [CrossRef]
6. A. Bozzola, L. Carroll, D. Gerace, I. Cristiani, and L. C. Andreani, “Optimising apodized grating couplers in a pure SOI platform to− 0.5 dB coupling efficiency,” Opt. Express 23(12), 16289–16304 (2015). [CrossRef]
7. W. Bogaerts, D. Taillaert, B. Luyssaert, P. Dumon, J. Van Campenhout, P. Bienstman, D. Van Thourhout, R. Baets, V. Wiaux, and S. Beckx, “Basic structures for photonic integrated circuits in silicon-on-insulator,” Opt. Express 12(8), 1583–1591 (2004). [CrossRef]
8. J. Zhang, L. Han, B. P. P. Kuo, and S. Radic, “Broadband angled arbitrary ratio SOI MMI couplers with enhanced fabrication tolerance,” J. Lightwave Technol. 38(20), 5748–5755 (2020). [CrossRef]
9. L. Vivien, A. Polzer, D. Marris-Morini, J. Osmond, J. M. Hartmann, P. Crozat, E. Cassan, C. Kopp, H. Zimmermann, and J. M. Fédéli, “Zero-bias 40Gbit/s germanium waveguide photodetector on silicon,” Opt. Express 20(2), 1096–1101 (2012). [CrossRef]
10. M. Romagnoli, S. Marconi, M. A. Giambra, A. Montanaro, V. Mišeikis, S. Soresi, S. Tirelli, P. Galli, F. Buchali, W. Templ, C. Coletti, and V. Sorianello, “High-data-rate photothermal effect graphene detector integrated in a SOI waveguide,” Broadband Access Communication Technologies XV. International Society for Optics and Photonics. 11711, 3 (2021). [CrossRef]
11. X. Li, J. Wang, Y. Liu, J. Chen, Y. Du, W. Wang, Y. Cai, J. Ma, and M. Yu, “Design of Ge 1-x Sn x-on-Si waveguide photodetectors featuring high-speed high-sensitivity photodetection in the C-to U-bands,” Appl. Opt. 59(25), 7646–7651 (2020). [CrossRef]
12. X. Li, Y. Liu, J. Wang, W. Wang, and M. Yu, “Germanium/germanium-tin heterojunction phototransistors: towards high-efficient,” International Conference on Optoelectronic and Microelectronic Technology and Application International Society for Optics and Photonics11617, 1161702 (2020).
13. O. Jafari, W. Shi, and S. J. I. P. T. L. LaRochelle, “Mach-Zehnder silicon photonic modulator assisted by phase-shifted Bragg gratings,” IEEE Photonics Technol. Lett. 32(8), 445–448 (2020). [CrossRef]
14. J. Zhou, J. Wang, L. Zhu, and Q. Zhang, “Silicon photonics for 100Gbaud,” J. Lightwave Technol. 39(4), 857–867 (2021). [CrossRef]
15. Y. Sobu, G. Huang, S. Tanaka, Y. Tanaka, Y. Akiyama, and T. Hoshida, “High-Speed optical digital-to-analog converter operation of compact two-segment all-silicon mach–zehnder modulator,” J. Lightwave Technol. 39(4), 1148–1154 (2021). [CrossRef]
16. R. Soref and B. Bennett, “Electrooptical effects in silicon,” IEEE J. Quantum Electron. 23(1), 123–129 (1987). [CrossRef]
17. A. Rahim, A. Hermans, B. Wohlfeil, D. Petousi, B. Kuyken, D. Van Thourhout, and R. Baets, “Taking silicon photonics modulators to a higher performance level: state-of-the-art and a review of new technologies,” Adv. Photonics 3(02), 024003 (2021). [CrossRef]
18. D. J. Thomson, Y. Hu, G. T. Reed, and J. M. Fedeli, “Low loss MMI couplers for high performance MZI modulators,” IEEE Photonics Technol. Lett. 22(20), 1485–1487 (2010). [CrossRef]
19. S. S. Azadeh, J. Nojić, A. Moscoso-Mártir, F. Merget, and J. Witzens, “Power-efficient lumped-element meandered silicon Mach-Zehnder modulators,” Silicon Photonics XV, International Society for Optics and Photonics, 11285, 112850C (2020).
20. Z. Ciou, K. Chung, S. Kao, C. Cheng, D. Huang, and G Lin, “Beyond 60-Gbit/s Modulation of Impedance Mismatched Silicon MZI Modulator,” 2021 IEEE 17th International Conference on Group IV Photonics (GFP), IEEE, 1–2 (2021).
21. M. Pantouvaki, P. Verheyen, J. De Coster, G. Lepage, P. Absil, and J. Van Campenhout, “56Gb/s ring modulator on a 300 mm silicon photonics platform,” 2015 European Conference on Optical Communication (ECOC), IEEE, 1–3 (2015).
22. J. Van Campenhout, M. Pantouvaki, P. Verheyen, S. Selvaraja, G. Lepage, H. Yu, W. Lee, J. Wouters, D. Goossens, M. Moelants, W. Bogaerts, and P. Absil, “Low-voltage, low-loss, multi-Gb/s silicon micro-ring modulator based on a MOS capacitor,” Optical Fiber Communication Conference, Optical Society of America, OM2E-4 (2012).
23. M. Sakib, P. Liao, C. Ma, R. Kumar, D. Huang, G. Su, X. Wu, S. Fathololoumi, and H. Rong, “A high-speed micro-ring modulator for next generation energy-efficient optical networks beyond 100 Gbaud,” CLEO: Science and Innovations, Optical Society of America, SF1C-3 (2021).
24. W. Franz, “Einfluß eines elektrischen Feldes auf eine optische Absorptionskante,” Zeitschrift für Naturforschung A 13(6), 484–489 (1958). [CrossRef]
25. L. V. Keldysh, “Behavior of non-metallic crystals in strong electric fields,” Sov. J. Exp. Theoretical Phys. 6, 763 (1958).
26. S. Jongthammanurak, J. Liu, K. Wadaa, D. D. Cannon, D. T. Danielson, D. Pan, L. C. Kimerling, and J. Michel, “Large electro-optic effect in tensile strained Ge-on-Si films,” Appl. Phys. Lett. 89(16), 161115 (2006). [CrossRef]
27. J. Liu, M. Beals, A. Pomerene, S. Bernardis, R. Sun, J. Cheng, L. C. Kimerling, and J. Michel, “Waveguide-integrated, ultralow-energy GeSi electro-absorption modulators,” Nat. Photonics 2(7), 433–437 (2008). [CrossRef]
28. D. Feng, S. Liao, H. Liang, J. Fong, B. Bijlani, R. Shafiiha, B. J. Luff, Y. Luo, J. Cunningham, A. V. Krishnamoorthy, and M. Asghari, “High speed GeSi electro-absorption modulator at 1550 nm wavelength on SOI waveguide,” Opt. Express 20(20), 22224–22232 (2012). [CrossRef]
29. S. A. Srinivasan, P. Verheyen, R. Loo, I. De Wolf, M. Pantouvaki, G. Lepage, S. Balakrishnan, W. Vanherle, P. Absil, and J. Van Campenhout, “50Gb/s C-band GeSi waveguide electro-absorption modulator,” Optical Fiber Communication Conference, Optical Society of America, Tu3D-7 (2016).
30. L. Mastronardi, M. Banakar, A. Z. Khokhar, N. Hattasan, T. Rutirawut, T. Domínguez Bucio, K. M. Grabska, C. Littlejohns, A. Bazin, G. Mashanovich, and F. Y. Gardes, “High-speed Si/GeSi hetero-structure electro absorption modulator,” Opt. Express 26(6), 6663–6673 (2018). [CrossRef]
31. A. Melikyan, N. Kaneda, K. Kim, Y. Baeyens, and P. Dong, “Differential drive I/Q modulator based on silicon photonic electro-absorption modulators,” J. Lightwave Technol. 38(11), 2872–2876 (2020).
32. J. F. Lampin, L. Desplanque, and F. Mollot, “Detection of picosecond electrical pulses using the intrinsic Franz–Keldysh effect,” Appl. Phys. Lett. 78(26), 4103–4105 (2001). [CrossRef]
33. X. Hu, D. Wu, Y. Zhang, H. Zhang, D. Chen, M. Liu, J. Liu, L. Wang, X. Xiao, and S. Yu, “110 Gbit/s NRZ and 160 Gbit/s PAM-4 GeSi Electro-Absorption Modulator,” 2022 Optical Fiber Communications Conference and Exhibition (OFC), IEEE, 1–3 (2022).
34. S. A. Srinivasan, M. Pantouvaki, S. Gupta, H. Chen, P. Verheyen, G. Lepage, G. Roelkens, K. Saraswat, D. Van Thourhout, P. Absil, and J. Van Campenhout, “56 Gb/s germanium waveguide electro-absorption modulator,” J. Lightwave Technol. 34(2), 419–424 (2016). [CrossRef]
35. Z. Liu, X. Li, C. Niu, J. Zheng, C. Xue, Y. Zuo, and B. Cheng, “56 Gbps high-speed Ge electro-absorption modulator,” Photonics Res. 8(10), 1648–1652 (2020). [CrossRef]
36. L. Vivien, J. Osmond, J. Fédéli, D. Marris-Morini, P. Crozat, J. Damlencourt, E. Cassan, Y. Lecunff, and S. Laval, “42 GHz pin Germanium photodetector integrated in a silicon-on-insulator waveguide,” Opt. Express 17(8), 6252–6257 (2009). [CrossRef]
37. G. Chen, Y. Yu, X. Xiao, and X. Zhang, “High speed and high power polarization insensitive germanium photodetector with lumped structure,” Opt. Express 24(9), 10030–10039 (2016). [CrossRef]
38. D. Wu, X. Hu, W. Li, D. Chen, L. Wang, and X. Xiao, “62 GHz germanium photodetector with inductive gain peaking electrode for photonic receiving beyond 100 Gbaud,” J. Semicond. 42(2), 020502 (2021). [CrossRef]
