M. N. Sakib

A 16 GHz silicon-based monolithic balanced photodetector with on-chip capacitors for 25 Gbaud front-end receivers

In this paper, a Germanium-on-Silicon balanced photodetector (BPD) with integrated biasing capacitors is demonstrated for highly compact monolithic 100 Gb/s coherent receivers or 25 Gbaud front-end receivers for differential or quadrature phase shift keying. The balanced photodetector has a bandwidth of approximately 16.2 GHz at a reverse bias of -4.5 V. The balanced photodetector exhibits a common mode rejection ratio (CMRR) of 30 dB. For balanced detection of return-to-zero (RZ) differential phase shift keying (DPSK) signal, the photodetector has a sensitivity of -6.95 dBm at the BER of 10(-12). For non-return-to-zero (NRZ) on off keying (OOK) signal, the measured BER is 1.0 × 10(-12) for a received power of -1.65 dBm at 25 Gb/s and 9.9 × 10(-5) for -0.34 dBm at 30 Gb/s. The total footprint area of the monolithic front-end receiver is less than 1 mm(2). The BPD is packaged onto a ceramic substrate with two DC and one RF connectors exhibits a bandwidth of 15.9 GHz.

Optical Front-End for Soft-Decision LDPC Codes in Optical Communication Systems

A low-complexity soft-decision 12.5 Gb/s optical receiver for decoding low-density parity-check codes reusing conventional hard-decision receivers is investigated. The simulated and experimental results show that the proposed optical receiver exhibits coding gains of 2.75 and 6.73 dB for post-forward-error-correction bit error rates of 10-4 and 10-9, respectively, over a hard-decision uncoded system for a 60 km single-mode optical fiber transmission. The soft-decision circuitry consumes approximately 5 W and is optimized to provide two confidence levels, one above and one below the hard-decision levels.

A Study of Error Correction Codes for PAM Signals in Data Center Applications

A study is presented through simulation and experiment on the proposed forward error correction (FEC) codes for data centers using higher order pulse amplitude modulation (PAM). The results highlight the tradeoffs in the adopted FEC approach for a fixed transmission link. Reed-Solomon (RS) and Bose-Chaudhuri-Hocquenghem (BCH) codes are considered in data center applications due to the low latency requirement budgeted for the encoding and decoding processes. Using Monte-Carlo and semi-analytical simulations, the signal to noise ratio requirement of PAM-N is obtained for a 500-m fiber transmission link at 100 Gb/s. For latency requirement under 100 ns, short-block RS codes offer possibly low complexity implementation with a pre-FEC bit error rate (BER) threshold at 8.8×10-5. On the other end, BCH codes provide higher coding gain up to 9.3 dB with a BER threshold at 2.5×10-3 at the expense of potentially longer decoding delay and complexity. An experimental investigation at 25 Gb/s for PAM-4 signal is performed to measure the actual net coding gain of the system. Results show that the performance of RS(578 514) code is within 1 dB of both BCH(3456 3084) and BCH(2464 2056) with 15% and 23% reduction in complexity, respectively.

45 Gb/s low complexity optical front-end for soft-decision LDPC decoders

In this paper a low complexity and energy efficient 45 Gb/s soft-decision optical front-end to be used with soft-decision low-density parity-check (LDPC) decoders is demonstrated. The results show that the optical front-end exhibits a net coding gain of 7.06 and 9.62 dB for post forward error correction bit error rate of 10(-7) and 10(-12) for long block length LDPC(32768,26803) code. The performance over a hard decision front-end is 1.9 dB for this code. It is shown that the soft-decision circuit can also be used as a 2-bit flash type analog-to-digital converter (ADC), in conjunction with equalization schemes. At bit rate of 15 Gb/s using RS(255,239), LDPC(672,336), (672, 504), (672, 588), and (1440, 1344) used with a 6-tap finite impulse response (FIR) equalizer will result in optical power savings of 3, 5, 7, 9.5 and 10.5 dB, respectively. The 2-bit flash ADC consumes only 2.71 W at 32 GSamples/s. At 45 GSamples/s the power consumption is estimated to be 4.95 W.

Low-Density Parity-Check Coding in Ultra-Wideband-Over-Fiber Systems

In this letter, the performance of an ultra-wideband (UWB)-over-fiber system with low-density parity-check (LDPC) coding is experimentally investigated and supported by a simulation study. The results show that short block length LDPC coding provides a coding gain between 5.75 and 8.5 dB for a code rate of 50% and 93.3%, respectively, compared to an uncoded UWB-over-fiber system at a bit-error rate of 10-8 after error correction.

Ultradense Silicon Photonic Interface for Optical Interconnection

A scalable ultradense silicon photonic interface with 61 compact vertical grating couplers on a pitch of 42.3 μm is designed and fabricated to match a pitch reducing optical fiber array (PROFA) hexagonal channel pattern. Experimental results show that the designed grating couplers with a minimum insertion loss of 4.5 dB and a 3-dB bandwidth of 50 nm are obtained. The crosstalk between different channels is less than -50 dB and the maximum loss difference across the PROFA interface is ~0.7 dB. High-speed data transmission indicates that a bandwidth density as large as 27 Tb/s/mm2 could be achieved within a footprint of 0.096 mm2, demonstrating the potential of silicon photonics for broadband optical interconnection.

A Silicon Photonic Integrated Packaged Coherent Receiver Front-End For Soft-Decision Decoding

In this paper, a packaged integrated coherent receiver and optical front-end for soft decision based on 25 Gbaud/s quadrature phase-shift keying (QPSK) is investigated for on-chip applications. The front-end consists of a 90° hybrid, balanced photodetectors, and unbalanced couplers monolithically integrated in a CMOS compatible silicon-on-insulator technology. The silicon photonic device is packaged onto a ceramic substrate with RF and dc connectors. The proposed front-end is an example of integration of system on chip. The integrated solution is able to provide 6.2 dB performance improvements over uncoded system without error correction. The front-end outperforms optical system with hard-decision forward error correction by 2.2 dB at the BER of 10-7.

A monolithic optical front-end for soft-decision error correction decoders

We investigate a monolithic optical front-end for soft-decision low-density parity-check (LDPC) decoders based on 100 Gb/s polarization division multiplexed quadrature shift keying (PM-QPSK) coherent detection.

Impact of RF noise on transmission performance of multiband OFDM UWB over fiber systems

We investigate the performance of multiband OFDM ultra wideband (UWB) signal over fiber system considering the impact of RF noise. A compensation technique is proposed to reduce RF noise impact.

Ultra-dense optical I/O interface for Silicon photonic interconnects

An ultra-dense optical off-chip I/O interface consisting of 61 grating couplers matching the pitch of a commercial two-dimensional fiber array enables tremendous bandwidth density on the order of tens of Tb/s/mm2 towards high throughput Silicon photonics.