James Harley

Modulator Bias and Optical Power Control of Optical Complex E-Field Modulators

We describe novel techniques for closed-loop control of inner and outer Mach-Zehnder (MZ) biases in a dual parallel MZ (DPMZ) optical modulator. We also present a new technique based on modulator bias dithers to monitor the optical power contribution of each RF data path. The latter is demonstrated in an I -Q power balance control loop. We show that the new control methods are extremely robust in presence of modulator non-idealities, such as finite extinction ratios and non-zero chirp. We also demonstrate these techniques to be largely independent of RF drive waveform characteristics. Mathematical derivations of control transfer curves are provided. These are supported by simulation and measurement results. Additionally, we present a simple technique for polarization power balance in a dual-polarization modulation format. Finally, we discuss some practical details related to the implementation of the control loops described in this work.

Electronic Pre-Compensation for a 10.7-Gb/s System Employing a Directly Modulated Laser

We investigate electronic pre-compensation for a 10.7-Gb/s system employing a directly modulated laser (DML). Initially, the nonlinear distortion resulting from the direct modulation of the laser is mitigated by pre-compensation based on reversal of the large signal rate equations and the use of digital signal processing to generate an appropriate modulating current. This concept is then utilized in a novel look-up table optimization scheme for electronic dispersion pre-compensation. Simulation results show pre-compensation of up to 350 km of single mode fiber at a required optical signal to noise ratio <; 16 dB for a bit error rate of 10-3 . It is shown that a 42.8 GSa/s digital to analog converter is sufficient for exploiting the full potential for electronic pre-compensation using a DML.

Electronic precompensation of the nonlinear distortion in a 10 Gb/s 4-ary ASK directly modulated laser

The nonlinear distortion resulting from the direct modulation of a semiconductor laser using 4-ary amplitude shift keying at 10 Gb/s is mitigated by precompensation based on the use of digital signal processing to generate an appropriate modulating current.

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).

Reducing the Complexity of Electronic Pre-compensation for the Nonlinear Distortions in a Directly Modulated Laser

A simplified expression relating the required input current for a directly modulated laser to a target output optical power is obtained and used experimentally in mitigating the laser nonlinear distortion by digital signal processing.