Stefan Lischke

High bandwidth, high responsivity waveguide-coupled germanium p-i-n photodiode

A novel waveguide-coupled germanium p-i-n photodiode is demonstrated which combines high responsivity with very high -3 dB bandwidth at a medium dark current. Bandwidth values are 40 GHz at zero bias and more than 70 GHz at -1 V. Responsivity at 1.55 µm wavelength ranges from 0.84 A/W at zero bias to 1 A/W at -1 V. Room temperature dark current density at -1 V is about 1 A/cm2. The high responsivity mainly results from the use of a new, low-loss contact scheme, which moreover also reduces the negative effect of photo carrier diffusion on bandwidth.

A 40 Gb/s Monolithically Integrated Linear Photonic Receiver in a

This letter presents the first 40 Gb/s monolithically integrated silicon photonics linear receiver (Rx) comprising a germanium photodiode (Ge-PD) and a linear transimpedance amplifier (TIA). Measured optical-electrical (O/E) 3 dB bandwidth (BW) of the Rx is 31 GHz. At 40 Gb/s, the Rx achieves a sensitivity of -3 dBm average optical input power with BER of 2.5×10-11. It operates at λ = 1.55 μm wavelength, uses 3.3 and 3.7 V power supplies, dissipates 275 mW of power, provides maximum differential output amplitude of 500 mVpp, and occupies an area of 3.2 mm2. The presented receiver achieves the highest bit rate among the published work in monolithically integrated silicon photonics receivers.

0.25~\mu {\rm m}

Waveguide-coupled, Ge lateral pin photodiodes featuring bandwidths of more than 50GHz and 40Gbps functionality are presented. Non-doping implantations are applied that allow one to reach this performance even under the effect of thermal steps acting when the diodes are integrated in a high-performance BiCMOS process. The effect of these implants is to lower the minority-carrier lifetime(s) and in this way, to reduce bandwidth degradation by minority-carrier diffusion in non-depleted, weakly doped regions.

BiCMOS SiGe:C Technology

The paper presents the first fully monolithic photonic-electronic single-polarization QPSK receiver for 56Gbps (28Gbaud). The receiver sub-system was realized in photonic BiCMOS technology and demonstrates integration capabilities for state-of-the-art coherent systems.

High-speed, waveguide Ge PIN photodiodes for a photonic BiCMOS process

Photonic BiCMOS is a novel technology for fabricating electronic-photonic integrated circuits. Broadband silicon photonics devices such as germanium photodiodes and depletion type Mach-Zehnder modulators were monolithically integrated in a high performance SiGe BiCMOS baseline process. Integration aspects and first examples of demonstrator circuits shall be reviewed.

Monolithic photonic-electronic QPSK receiver for 28Gbaud

In this paper, a monolithically integrated segmented linear driver and Mach-Zehnder modulator (MZM) are presented. The transmitter is fabricated in electronic-photonic integrated circuit 0.25-μm SiGe:C BiCMOS technology, with fT/fmax = 190 GHz. The driver and the modulator are divided into 16 segments and the MZM phase shifter has a total length of 6.08 mm. The segmented driver delivers a maximum of 4 Vpp differentially, featuring a gain of 13 dB and total harmonic distortion below 5%. Electro-optical time-domain measurements using PAM-4 modulation format are performed, demonstrating optical eye-diagrams up to 25 Gbaud. The electro-optical bandwidth of the transmitter is 18 GHz. The power dissipation of the driver is 1.5 W, resulting in an energy per bit of 30 pJ/bit at 50 Gb/s. The reported optical transmitter demonstrates for the first time an implementation of a linear driver integrated with an MZM in a Si monolithic process.

High-performance BiCMOS Si photonics platform

Slot waveguide ring resonators appear promising candidates for several applications in silicon photonics. Strong field confinement, high device tunability, and low power consumption are beneficial properties compared with strip waveguides. Slot waveguide ring resonators suffer, however, from rather low optical quality factors due to optical losses. This letter proposes and experimentally demonstrates a novel concept based on a partially slotted ring and a strip-to-slot mode converter. An exceptional high quality factor of ~105 has been measured.

A Monolithically Integrated Segmented Linear Driver and Modulator in EPIC 0.25-

In this work, a monolithically integrated segmented driver and Mach-Zehnder modulator (MZM) in 0.25 μm SiGe:C BiCMOS technology is presented. The driver and the modulator are divided in 16 segments and the MZM has a total length of 6.08 mm. The driver has a maximum gain of 14.5 dB. Electro-optical time-domain measurements were performed and an optical eye-diagram with more than 13 dB of extinction ratio at 28 Gb/s is demonstrated. The driver dissipates a total of 2 W of DC power. To the best knowledge of the authors, the presented work shows the highest extinction ratio achieved at 28 Gb/s in silicon modulators.

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A novel monolithic opto-electronic clock converter integrated in a photonic SiGe-BiCMOS technology is presented, which turns an ultrashort optical pulse train generated by a hybrid mode-locked laser into a low-jitter electrical square wave with sharp transitions. The integrated circuit includes optical waveguides as well as grating couplers, a high-bandwidth (> 30 GHz) Ge-photodiode, a frequency divider-by-two implemented by SiGe bipolar transistors, photodiode characterization circuits and an optical monitoring path. The integrated circuit has been successfully tested at laser pulse repetition rates of up to 10 GHz. At this pulse repetition rate, the generated 5 GHz electrical square wave signal features a wideband phase noise floor <;-160 dBc/Hz and an jitter tj <; 1 fs while integrating the phase noise at offset frequencies between 2 kHz and 30 MHz.

m SiGe:C BiCMOS Platform

Monolithic integration of photonic functionality in the frontend-of-line (FEOL) of an advanced microelectronics technology is a key step towards future communication applications. This combines photonic components such as waveguides, couplers, modulators, and photo detectors with high-speed electronics plus shortest possible interconnects crucial for high-speed performance. Integration of photonics into CMOS FEOL is therefore in development for quite some time reaching 90nm node recently [1]. However, an alternative to CMOS is high-performance BiCMOS, offering significant advantages for integrated photonics-electronics applications with regard to cost and RF performance. We already presented results of FEOL integration of photonic components in a high-performance SiGe:C BiCMOS baseline to establish a novel, photonic BiCMOS process. Process cornerstone is a local-SOI approach which allows us to fabricate SOI-based, thus low-loss photonic components in a bulk BiCMOS environment [2]. A monolithically integrated 10Gbit/sec Silicon modulator with driver was shown here [3]. A monolithically integrated 25Gbps receiver was presented in [4], consisting of 200GHz bipolar transistors and CMOS devices, low-loss waveguides, couplers, and highspeed Ge photo diodes showing 3-dB bandwidth of 35GHz, internal responsivity of more than 0.6A/W at λ= 1.55μm, and ~ 50nA dark current at 1V. However, the BiCMOS-given thermal steps cause a significant smearing of the Germanium photo diodes doping profile, limiting the photo diode performance. Therefore, we introduced implantation of non-doping elements to overcome such limiting factors, resulting in photo diode bandwidths of more than 50GHz even under the effect of thermal steps necessary when the diodes are integrated in a high performance BiCMOS process.