Shannon M. Madison

Uni-traveling-carrier variable confinement waveguide photodiodes

Uni-traveling-carrier waveguide photodiodes (PDs) with a variable optical confinement mode size transformer are demonstrated. The optical mode is large at the input for minimal front-end saturation and the mode transforms as the light propagates so that the absorption profile is optimized for both high-power and high-speed performance. Two differently designed PDs are presented. PD A demonstrates a 3-dB bandwidth of 12.6 GHz, and saturation currents of 40 mA at 1 GHz and 34 mA at 10 GHz. PD B demonstrates a 3-dB bandwidth of 2.5 GHz, a saturation current greater than 100 mA at 1 GHz, a peak RF output power of + 19 dBm, and a third-order output intercept point of 29.1 dBm at a photocurrent of 60 mA.

Slab-coupled optical waveguide photodiode

We report the first high-current photodiode based on the slab-coupled optical waveguide concept. The device has a large mode (5.8 times 7.6 mum) and ultra-low optical confinement (Gamma ~ 0.05%), allowing a 2-mm absorption length. The maximum photocurrent obtained was 250 mA (R = 0.8-A/W) at 1.55 mum.

Slab-coupled optical waveguide (SCOW) based optoelectronic oscillator (OEO)

We demonstrate a 3-GHz ultralow phase-noise (measurement limited <;-132 dB/Hz at 10 kHz offset) amplifier-free optoelectronic oscillator with significantly suppressed sidemode spurs (<;-140 dB) employing a slab-coupled optical waveguide external-cavity laser and photodiode.

Compact external-cavity semiconductor mode-locked laser with quantum-well-intermixed modulator and saturable absorber

We demonstrate a slab-coupled optical waveguide external-cavity mode-locked laser having unique bandedges for the amplifier, modulator and saturable absorber elements. An average output power of 50 mW and timing jitter of 254fs is achieved at 1.5-GHz.

Third-order intermodulation distortion characterization of variable confinement slab-coupled optical waveguide photodiodes

We report two-tone third-order intermodulation distortion (IMD3) characterization of a uni-traveling-carrier waveguide photodiode which uses a horizontal taper mode size transformer to vary the optical confinement with length. Fixed confinement waveguide photodiodes are also characterized.

Limits to Maximum Absorption Length in Waveguide Photodiodes

The maximum photocurrent, power dissipation, and linearity of waveguide photodiodes are limited by the length over which the input optical power is absorbed. This absorption length is determined by the absorption coefficient of the absorbing layer material (αo), the optical confinement factor (Γ), and the excess loss coefficient (αi). In this paper, we analyze the fundamental limits to maximizing the absorption length and demonstrate a new waveguide photodiode structure that approaches these limits. The new structure is referred to as a slab-coupled optical waveguide photodiode (SCOWPD) and is realized in the InGaAsP/InP material system. Assuming 100% coupling efficiency, the SCOWPD has an ultralow optical confinement factor and a low excess loss coefficient, both calculated from measurements, of Γ = 0.069% and αi = 1.65 cm-1, respectively. This results in a 1/e absorption length of 2.1 mm. The SCOWPD exhibits an external responsivity of 0.8 A/W and a maximum photocurrent of 250 mA at a wavelength of 1.55 μm.

Propagation Delay of Waveguide Photodetector

Optical phase locked loop (OPLL) photonic integrated circuits (PIC) are critical for the high dynamic range phase modulated RF/photonic links. They provide for linear phase demodulation. A challenge for implementing the OPLL PICs is how to reduce the loop propagation delay. In this paper we analyze the delay of a waveguide photodetector, which is a critical component of an OPLL. We also introduce and experimentally validate a counter propagating photodetector device concept. This enables the elimination of the propagation delay due to the finite length of a waveguide photodetector.

High-power and high-speed waveguide uni-traveling-carrier photodiodes for microwave photonics applications

Uni-traveling-carrier waveguide photodiodes (PDs) with variable optical confinement mode size transformers are demonstrated. For these waveguide PDs, the optical mode is large at the input for minimal front-end saturation. The mode transforms as the light propagates so that the absorption profile is optimized for both high-power and high-speed performance.

Microwave photonic applications of slab-coupled optical waveguide devices

The semiconductor slab-coupled optical waveguide (SCOW) concept is a versatile device platform that has enabled new classes of high-power, low-noise single-frequency lasers, mode-locked lasers, optical amplifiers, and photodiodes for analog optical links and photonic analog-to-digital converters.