Alexander S. Hastings

Photodetector Nonlinearities Due to Voltage-Dependent Responsivity

A newly quantified photodiode nonlinearity is derived from a previously known bias voltage-dependent responsivity. For an InGaAs p-i-n photodiode, measured harmonic distortion is shown to be dominated by this derived nonlinearity mechanism. It is also shown that electron ionization in the depletion region of the photodiode is the source of the voltage-dependent responsivity.

Photodiode linearity requirements for radio-frequency photonics and demonstration of increased performance using photodiode arrays

The impact that photodiode nonlinearities have on intensity-modulation direct-detection analog photonic links is described. The second- and third-order linearity requirements for photodiodes, quantified in terms of output intercept points, are calculated. Measured data at 1 GHz for a high-current (60-mA) partially-depleted-absorber photodiode are presented. A four-photodiode 26-mA array at 5 MHz is demonstrated to achieve modulation-limited third-order performance and a second-harmonic output intercept point of 84 dBm.

Comparison of photodiode nonlinearity measurement systems

Photodiode nonlinearity measurements using one-, two- and three-tone measurement systems are compared with each other, to investigate the comparison accuracy between setups. The mathematical relationship between each setup is analyzed, and data on multiple devices are compared to find under which conditions the measurements are comparable. It is shown that the three measurement systems can be used interchangeably only when the distortion adheres to the expected mathematical slopes.

Minimizing Photodiode Nonlinearities by Compensating Voltage-Dependent Responsivity Effects

Two voltage-dependant responsivity effects, impact ionization and Franz-Keldysh oscillations, are shown to have opposing effects at certain wavelengths in p-i-n photodiodes. It is shown that these two effects can compensate each other and minimize photodiode nonlinearities when optimized with respect to wavelength and bias voltage.

Cancellation of photodiode-induced second harmonic distortion using single side band modulation from a dual parallel Mach-Zehnder

We have theoretically and experimentally investigated using a dual parallel Mach-Zehnder modulator (DP-MZM) in an RF photonic link to cancel the second harmonic distortion due to the photodiode. Biasing the DP-MZM for single sideband modulation, the second harmonic generated by the DP-MZM can be set out of phase with the second harmonic generated at the photodiode. We measure the output intercept point of the second harmonic distortion of the link to be 55.3 dBm, which is an improvement of over 32 dB as compared to only the photodiode.

Measurement of intermodulation distortion in high-linearity photodiodes

Accurately characterizing third order intermodulation distortion (IMD3) in high-linearity photodiodes is challenging. Two measurement techniques are evaluated-a standard two-tone measurement and a more complicated three-tone measurement technique to measure IMD3. A model of the measurement system is developed and used to analyze the limitations of the two techniques in determining the distortion of highly linear photodiodes. Experimental validation is provided by comparing the simulation trends with IMD3 results measured on two types of waveguide photodiodes: 1) an InP based uni-traveling-carrier (UTC) photodiode and 2) a Ge n-i-p waveguide photodetector on Silicon-on-Insulator (SOI) substrate.

RF Power Conversion Efficiency of Photodiodes Driven by Mach–Zehnder Modulators

A comprehensive analysis supported by experimental results is provided for RF and microwave power conversion efficiency (PCE) of photodiodes driven by optical signals with either shaped or pure sinusoidal intensity-envelopes where the shaping is performed with a Mach-Zehnder modulator (MZM). It is shown that optical envelope-shaping provides a significantly improved maximum theoretical PCE of 67% as compared to 50% for sinusoidal intensity-envelopes. Practical PCEs of 40.5%-53.5% have been achieved as compared to previously published efficiencies in the 32%-41% range. The results demonstrate that high-current photodiodes can be used as efficient wideband high-power output stages in microwave photonic distribution systems leading to less complex and more efficient antenna array backplanes.

RF Characterization of Zero-Biased Photodiodes

The characteristics of zero-biased InGaAs p-i-n photodiodes were studied for use as optical transducers in an in situ phased array radar calibrator. Radio frequency (RF) operation is especially important for the intended application in which the zero-biased photodiodes drive patch antennas embedded in a radome. The photodiodes act as sources for real-time calibration of the phase and amplitude of each array element and will operate with only optical input from a modulated optical fiber link. Unfortunately, little is known of the RF performance of photodiodes operated without voltage bias. In this paper, both the dc and RF performance of a particular photodiode were studied to determine the optimum operating conditions and to understand the type and severity of any limitations.

53.5% photodiode RF power conversion efficiency

A record 53.5% RF power conversion efficiency is reported for a photodiode delivering 24.4 dBm output power. This is achieved by optimized photodiode design, optical intensity-envelope shaping with a Mach-Zehnder modulator and photodiode signal compression.

Impact of voltage-dependent responsivity on photodiode non-linearity

The change of responsivity with applied bias voltage of an InGaAs/InP modified charge compensated uni-traveling carrier photodiode has been studied over a wide range of input wavelengths. The measured wavelength-dependence suggests that the primary reasons for the observed characteristics are both the Franz-Keldysh effect and impact ionization. Based on the experimental results we estimated a photodiodepsilas low-frequency third order intercept point (IP3) of 61 dBm when choosing an appropriate input wavelength.