High-speed performance of a TDFA-band micro-ring resonator modulator and detector.

We demonstrate a silicon-on-insulator micro-ring resonator (MRR) modulator and defect-mediated (DM) detector operating at a wavelength near 2 µm for use in the thulium doped fiber amplifier wavelength band. The MRR modulator was critically coupled with an unbiased notch-depth of 20 dB and Q-factor of 4700. The resonance shift under reverse bias was 23 pm/V with a calculated VπLπ of 2.2 to 2.6 V·cm from -1 to -8 V, respectively. Simulations are in good agreement with the measured data. The experimental modulation bandwidth was 12.5 GHz, limited by the response of the commercial external detector used for this measurement. The DM detector was operated in avalanche mode, had 1.97 µm wavelength responsivities of 0.04 and 0.14 A/W, and had bandwidths greater than 16 and 7.5 GHz at -15 and -30 V biases, respectively. Large-signal measurement demonstrated open eye-diagrams at 5, 10, and 12.5 Gbps for the DM detector and also for an optical link consisting of the modulator and detector integrated on the same silicon chip.

Resonance control of a silicon micro-ring resonator modulator under high-speed operation using the intrinsic defect-mediated photocurrent.

A method to stabilize the resonance wavelength of a depletion-type silicon micro-ring resonator modulator during high-speed operation is described. The method utilizes the intrinsic defect-mediated photo-absorption of a silicon waveguide and results in a modulator chip fabrication process that is free of heterogeneous integration (for example using germanium), thus significantly reducing the complexity and cost of manufacture. Residual defects, present after p-n junction formation, are found to produce an adequate photocurrent for use as a feedback signal, while an integrated heater is used to compensate for thermal drift via closed-loop control. The photocurrent is measured by a source-meter, which simultaneously provides a DC bias to the integrated heater during high-speed operation. A drop-port or an integrated extrinsic detector is not needed. This feedback control method is experimentally demonstrated via a computer-aided proportional-integral-differential loop. The resonance locking is validated for 12.5 Gb/s intensity modulation in a back-to-back bit-error-rate measurement. The stabilization method described is not limited to a specific modulator design and is compatible with speeds greatly in excess of 12.5 Gb/s, in contrast to the bandwidth limitation of other stabilization methods that rely on intrinsic photo-carrier generation through non-linear processes such as two-photon-absorption. Further, the use of intrinsic defects present after standard fabrication insures that no excess loss is associated with this stabilization method.

Digital signal processing for fiber nonlinearities [Invited].

This paper reviews digital signal processing techniques that compensate, mitigate, and exploit fiber nonlinearities in coherent optical fiber transmission systems.

Monolithic silicon waveguide photodiode utilizing surface-state absorption and operating at 10 Gb/s.

We have fabricated a waveguide integrated monolithic silicon infrared detector. The photodiode consists of a p-i-n junction across a silicon-on-insulator (SOI) rib waveguide. Absorption is due to surface-states at the silicon/air interface of the waveguide. A 2 mm long detector shows a response of 0.045 A/W (calculated as a function of coupled light) and is capable of operation at 10 Gb/s at a reverse bias voltage of 2 V.

400 Gbit/s single-carrier and 1 Tbit/s three-carrier superchannel signals using dual polarization 16-QAM with look-up table correction and optical pulse shaping.

A 448 Gbit/s single-carrier dual-polarization 16-ary quadrature-amplitude-modulation (DP 16-QAM) signal and a 1.206 Tbit/s three-carrier DP 16-QAM signal are demonstrated using look-up table (LUT) correction and optical pulse shaping. The LUT correction is used to mitigate the effects of transmitter-based pattern-dependent distortion due to the high symbol rates. A programmable optical filter is employed to narrow the modulated signal spectrum and thereby enhance the spectral efficiency and reduce the requirements on the receiver bandwidth and analog-to-digital converter sampling rate. By combining these techniques, the back-to-back required optical signal-to-noise ratios are 26.6 dB and 27.2 dB for BER = 10(-3), and transmission over 1200 and 1500 km of standard single-mode fiber with EDFA amplification was achieved for the 448 Gbit/s signal (12% forward error correction (FEC) overhead) and 1.206 Tbit/s signal (20% FEC overhead), respectively.

Reducing the complexity of perturbation based nonlinearity pre-compensation using symmetric EDC and pulse shaping.

Perturbation based nonlinearity pre-compensation has been performed for a 128 Gbit/s single-carrier dual-polarization 16-ary quadrature-amplitude-modulation (DP 16-QAM) signal. Without any performance degradation, a complexity reduction factor of 6.8 has been demonstrated for a transmission distance of 3600 km by combining symmetric electronic dispersion compensation and root-raised-cosine pulse shaping with a roll-off factor of 0.1. Transmission over 4200 km of standard single-mode fiber with EDFA amplification was achieved for the 128 Gbit/s DP 16-QAM signals with a forward error correction (FEC) threshold of 2 × 10(-2).

10 Gbps silicon waveguide-integrated infrared avalanche photodiode.

We have fabricated monolithic silicon avalanche photodiodes capable of 10 Gbps operation at a wavelength of 1550 nm. The photodiodes are entirely CMOS process compatible and comprise a p-i-n junction integrated with a silicon-on-insulator (SOI) rib waveguide. Photo-generation is initiated via the presence of deep levels in the silicon bandgap, introduced by ion implantation and modified by subsequent annealing. The devices show a small signal 3 dB bandwidth of 2.0 GHz as well as an open eye pattern at 10 Gbps. A responsivity of 4.7 ± 0.5 A/W is measured for a 600 µm device at a reverse bias of 40 V.

Generation and transmission of DPSK signals using a directly modulated passive feedback laser.

The generation of differential-phase-shift keying (DPSK) signals is demonstrated using a directly modulated passive feedback laser at 10.709-Gb/s, 14-Gb/s and 16-Gb/s. The quality of the DPSK signals is assessed using both noncoherent detection for a bit rate of 10.709-Gb/s and coherent detection with digital signal processing involving a look-up table pattern-dependent distortion compensator. Transmission over a passive link consisting of 100 km of single mode fiber at a bit rate of 10.709-Gb/s is achieved with a received optical power of -45 dBm at a bit-error-ratio of 3.8 × 10(-3) and a 49 dB loss margin.

Pulse shaping for 112 Gbit/s polarization multiplexed 16-QAM signals using a 21 GSa/s DAC.

The implications of increasing the symbol rate for a given digital-to-analog converter (DAC) sampling rate are investigated by considering the generation of 112 Gbit/s PM 16-QAM signals (14 Gsym/s) using a 21 GSa/s DAC with 6-bit resolution.

Electronic dispersion pre-compensation for 10.709-Gb/s using a look-up table and a directly modulated laser.

A novel electronic dispersion pre-compensation scheme for a directly modulated laser is described and experimentally demonstrated for transmission distances beyond 200 km using a low-cost laser packaged for 2.5-Gb/s while operated at 10.709-Gb/s. A single look-up-table (LUT) for the drive current is designed to mitigate the effects of fiber dispersion, the intrinsic nonlinear modulation response of the laser, and the laser package. Experimental results show that an 11-bit LUT can compensate the dispersion of 202 km of standard single mode fiber with a required optical-signal-to-noise-ratio of 18.61 dB at a bit error ratio of 3.8 × 10(-3).

Application of a passively mode-locked quantum-dot Fabry-Perot laser in 40 Gb/s all-optical 3R regeneration.

The application of a mode-locked quantum-dot Fabry-Perot (QD-FP) laser in a wavelength preserving all-optical 3R regenerator is demonstrated at 40 Gb/s. The 3R regenerator consists of a QD-FP laser for low-timing jitter clock recovery, cross-phase modulation based retiming, and self-phase modulation based reshaping. The performance of the alloptical 3R regenerator is assessed experimentally in terms of the Q-factor, timing jitter and bit-error ratio.

Low-timing-jitter all-optical clock recovery for 40 Gbits/s RZ-DPSK and NRZ-DPSK signals using a passively mode-locked quantum-dot Fabry-Perot semiconductor laser.

We investigate experimentally all-optical clock recovery for return-to-zero (RZ) and nonreturn-to-zero (NRZ) differential phase-shift keying (DPSK) signals at 40 Gbits/s using a passively mode-locked quantum-dot Fabry-Perot (QD-FP) semiconductor laser. The QD-FP laser exhibits a beat spectrum linewidth of 80 kHz, which enables a recovered clock signal with a root-mean-square timing jitter of 160 fs for the RZ-DPSK signal and 240 fs for the NRZ-DPSK signal. The timing jitter of the recovered clock signal is characterized for different values of the input signal power and the input signal optical signal-to-noise ratio.