Meredith N. Hutchinson

Mitigation of Photodiode Induced Even-Order Distortion in Photonic Links With Predistortion Modulation

A new class of predistortion techniques for suppressing photodiode generated even-order distortion is presented. Modulation induced distortions can be generated to cancel the photodiode even-order contributions. This method is described conceptually, theoretically, and experimentally in a generalized fashion to include intensity-, phase-, and polarization-modulation implementations. Measured suppression of photodiode second-order distortion upwards of 34 dB is demonstrated with frequencies ranging from 1 to 35 GHz.

Suppression of even-order photodiode distortions via predistortion linearization with a bias-shifted Mach-Zehnder modulator

A new technique to cancel photodiode-induced even-order distortion in microwave photonic links is demonstrated. A single Mach-Zehnder modulator, biased slightly away from the quadrature point, is shown to suppress photodiode second-order intermodulation distortion in excess of 40 dB without affecting the fundamental power. The technique is theoretically described with supporting experimental results.

Analysis of magnitude and relative phase of photodiode IMD2 using amplitude matched MZM-distortion cancellation technique.

We present a detailed look at using Mach-Zehnder modulator generated distortion for identifying the magnitude and relative sign of photodiode generated second order intermodulation distortion (IMD2). Previous discussions introduced the concept for characterizing a test device. Analysis is expanded to IMD2 as a function of voltage, photocurrent and frequency.

Simulation of a partially depleted absorber (PDA) photodetector.

We use a 2D drift-diffusion model to study the nonlinear response of a partially depleted absorber (PDA) phododetector. The model includes external loading, incomplete ionization, the Franz-Keldysh effect, and history-dependent impact ionization. It also takes into account heat flow in the device. With all these effects included, we obtain excellent agreement with experiments for the responsivity and for the harmonic power at different modulation frequencies. The role of these different physical effects is elucidated, and we find that both the Franz-Keldysh effect and the load resistance play a key role in generating higher harmonic power at larger reverse biases. Increasing the size of the p-region absorption layers reduces the impact of the Franz-Keldysh effect. Decreasing the effective load resistance also decreases the higher harmonic powers. We also show that the model can suggest design changes that will improve device performance.

Procedure for aligning polarization modulator link for amplitude modulation applications.

A procedure is detailed for aligning the transmitted output states of a polarization modulated signal to the analyzer states of a polarizing discriminator in an analog photonic link. The steps in the procedure insure optimal amplitude modulation in the link. Experimental results are presented for biasing in two ways: either the DC bias on the modulator or a rotatable half-wave plate can be used. The corresponding theory is included.

Determining the magnitude and relative phase of photodiode IMD2 using amplitude matched MZM-distortion cancellation technique

We characterize photodiode-induced second-order intermodulation distortion (IMD2) implementing a new Mach-Zehnder modulator (MZM) distortion cancellation technique. The magnitude and relative phase of photodiode IMD2 can be determined by measurement of an intensity-modulated direct-detection (IMDD) link at the cancellation condition. The magnitude is also found through photodiode fundamental frequency response and calculated second-order output intercept point (OIP2). Experimental results show that the IMDD technique is suitable for rapid amplitude estimation, while also providing phase information for the photodiode non-linearity.

Power photodiodes for high dynamic range photonic links.

High-power photodiode applications for multioctave high dynamic range links are presented. A review of modulator and photodiode distortion analysis is given as well as an introduction to polarization-dependent loss distortion as it pertains to such systems. A new analysis of the photodiode distortion contributed degradation of spurious free dynamic range (SFDR) is developed. Experimental data covers high-power photodiodes for zero-bias high dynamic range links, showing significant improvement in SFDR. A link is presented showing the degradation of link performance when polarization-dependent loss is added into the system. A summary of state-of-the-art device performance is covered as well as the outlook on future applications for power photodiodes in analog photonic links requiring high SFDR.

Characterization of Photodiode Nonlinearities by Output Frequency Analysis

We introduce a new technique for characterizing nonlinear behavior in photodiodes and illustrate its use for second order intermodulation distortion (IMD). For a given operating point (bias voltage and dc current), we construct a frequency-dependent nonlinear coefficient and plot it versus the output frequency of the IMD product. We find that for large ranges of operating points, the nonlinear coefficient falls on the same single curve, regardless of whether it was a sum, high difference, or low difference frequency plan that created the tone. Additionally, we found evidence of scaling: Regions in which changes in the universal curve due to a change in bias voltage can be cancelled by a systematic change in the dc current. That is, the nonlinear coefficients for a family of bias/current pairs fall on the same curve in these regions. This method shows that standard characterization of nonlinearities, such as finding intercept points, can be efficiently organized. Furthermore, it implies that comparison of nonlinear behavior of different photodiodes can be made directly on a uniform basis.

Polarization-Dependent Loss in Polarization Modulated Photonic Links: Model and Experiment

We investigate the effect of a discrete source of polarization-dependent loss in polarization-modulated optical links, using a Jones- and Stokes-vector description. We derive an expression for the output photocurrent in terms of the launch state and the link characteristics. We verify the theoretical description with an experimental investigation of a photonic link into which controlled polarization-dependent losses are introduced. The experimental results confirm a surprising theoretical conclusion: the distortion caused by polarization-dependent loss is equivalent to a simple system phase shift.

Computational Study of Amplitude-to-Phase Conversion in a Modified Unitraveling Carrier Photodetector

We calculate the amplitude-to-phase (AM-to-PM) noise conversion in a modified unitraveling carrier photodetector. We obtained two nulls as measured in the experiments, and we explain their origin. The nulls appear due to the transit time variation when the average photocurrent varies, and the transit time variation is due to the change of electron velocity when the average photocurrent varies. We also show that the AM-to-PM conversion coefficient depends only on the pulse energy and is independent of the pulse duration when the duration is less than 500 fs. When the pulse duration is larger than 500 fs, the nulls of the AM-to-PM conversion coefficient shift to larger average photocurrents. This shift occurs because the increase in that pulse duration leads to a decrease in the peak photocurrent. The AM-to-PM noise conversion coefficient changes as the repetition rate varies. However, the repetition rate does not change the AM-to-PM conversion coefficient as a function of input optical pulse energy. The repetition rate changes the average photocurrent. We propose a design that would in theory improve the performance of the device.