62 GHz germanium photodetector with inductive gain peaking electrode for photonic receiving beyond 100 Gbaud

Silicon photonics has attracted a great deal of interest for integrated photonics systems due to its large-scale electronics-photonics integration on a chip by leveraging the fabrication process of the complementary-metal-oxide semiconductor(CMOS)foundries[1−5].Germanium-on-silicon(Ge-on-Si)waveguide photodetector(PD)is an indispensable building block of silicon photonics technology which requires high sensitivity.

408 Gbit/s PAM-8 sidewall-doped germanium-silicon photodetector

Based on the 90 nm silicon photonics commercial foundry,sidewall-doped germanium-silicon photodetectors(PDs)are designed and fabricated.The large designed overlap between the optical field and electric field achieves high responsivity while retaining high-speed performance.Even including the loss due to optical fiber coupling,the PD demonstrates an external responsivity greater than 0.55 A/W for transverse magnetic(TM)polarization and 0.65 A/W for transverse electric(TE)polarization at 1530 nm.A flat responsivity spectrum of>0.5 A/W is achieved up to 1580 nm for both polarizations.Their internal responsivities can exceed 1 A/W in the C+L optical communication bands.Furthermore,with the aid of a 200 mm wafer-level test and analysis,the overall PDs of 26 reticles have a 3 dB optoelectrical bandwidth>50 GHz and a dark current<10 nA at a-3 V bias voltage.Finally,the eye diagram performances under TE and TM polarizations,various modulation formats,and different input wavelengths are comprehensively investigated.The clear open electrical eye diagrams up to 120,130,140,and 150 Gbit/s nonreturn-to-zero are experimentally attained at a photocurrent of 1 m A.To the best of our knowledge,this is the first time that single-lane direct detection of record-high-speed 200,224,256,and290 Gbit/s four-level pulse amplitude modulation(PAM)and 300,336,384,and 408 Gbit/s eight-level PAM optical signals has been experimentally achieved.

High-speed and high-power germanium photodetector with a lateral silicon nitride waveguide

Up to now, the light coupling schemes of germanium-on-silicon photodetectors(Ge-on-Si PDs) could be divided into three main categories:(1) vertical(or normal-incidence) illumination, which can be from the top or back of the wafer/chip, and waveguide-integrated coupling including(2) butt coupling and(3) evanescent coupling. In evanescent coupling the input waveguide can be positioned on top, at the bottom, or lateral to the absorber. Here,to the best of our knowledge, we propose the first concept of Ge-on-Si PD with double lateral silicon nitride(Si_(3)N_(4)) waveguides, which can serve as a novel waveguide-integrated coupling configuration: double lateral coupling. The Ge-on-Si PD with double lateral Si_(3)N_(4) waveguides features uniform optical field distribution in the Ge region, which is very beneficial to improving the operation speed for high input power. The proposed Ge-on-Si PD is comprehensively characterized by static and dynamic measurements. The typical internal responsivity is evaluated to be 0.52 A/W at an input power of 25 mW. The equivalent circuit model and theoretical 3 dB optoelectrical(OE) bandwidth investigation of Ge-on-Si PD with lateral coupling are implemented. Based on the small-signal(S21) radio-frequency measurements, under 4 mA photocurrent, a 60 GHz bandwidth operating at-3 V bias voltage is demonstrated. When the photocurrent is up to 12 mA, the 3 dB OE bandwidth still has 36 GHz. With 1 mA photocurrent, the 70, 80, 90, and 100 Gbit/s non-return-to-zero(NRZ) and 100,120, 140, and 150 Gbit/s four-level pulse amplitude modulation clear openings of eye diagrams are experimentally obtained without utilizing any offline digital signal processing at the receiver side. In order to verify the highpower handling performance in high-speed data transmission, we investigate the eye diagram variations with the increase of photocurrents. The clear open electrical eye diagrams of 60 Gbit/s NRZ under 20 mA photocurrent are also obtained. Overall, the proposed lateral Si_(3)N_(4) waveguide structure is flexibly extendable to a light coupling configuration of PDs, which makes it very attractive for developing high-performance silicon photonic integrated circuits in the future.

67 GHz light-trapping-structure germanium photodetector supporting 240 Gb/s PAM-4 transmission

A light-trapping-structure vertical Ge photodetector(PD)is demonstrated.In the scheme,a 3μm radius Ge mesa is fabricated to constrain the optical signal in the circular absorption area.Benefiting from the light-trapping structure,the trade-off between bandwidth and responsivity can be relaxed,and high opto-electrical bandwidth and high responsivity are achieved simultaneously.The measured 3 d B bandwidth of the proposed PD is around67 GHz,and the responsivity is around 1.05 A/W at wavelengths between 1520 and 1560 nm.At 1580 nm,the responsivity is still over 0.78 A/W.A low dark current of 6.4 n A is also achieved at-2 V bias voltage.Based on this PD,a clear eye diagram of 100 GBaud four-level pulse amplitude modulation(PAM-4)is obtained.With the aid of digital signal processing,240 Gb/s PAM-4 signal back-to-back transmission is achieved with a bit error ratio of 1.6×10^(-2).After 1 km and 2 km fiber transmission,the highest bit rates are 230 and 220 Gb/s,respectively.