Nobuhiro Nunoya

High Power Silicon-Germanium Photodiodes for Microwave Photonic Applications

We demonstrate high current operation of an evanescently coupled Ge waveguide n-i-p photodetector grown on top of a Si rib waveguide. A 7.4 μm × 500 μm device was found to dissipate 1.003 W of power (125.49 mA at -8 V). 2-D thermal simulations of the device show that the relatively high thermal conductivities of the intrinsic Ge region and the p+ doped Si layer result in efficient heat transfer and hence, lower absorber temperatures when compared to a similar InP based waveguide photodiode. Additionally, to determine the feasibility of these devices for analog photonic applications, we performed large signal and small signal radio frequency (RF) measurements as well as linearity measurements. At 1 GHz and 40 mA of photocurrent, a third order output intercept point (OIP3) of 36.49 dBm is measured. The maximum RF power extracted at 1 GHz is 14.17 dBm at 60 mA of photocurrent and 7 V reverse bias.

Three-tone characterization of high-linearity waveguide uni-traveling-carrier photodiodes

The IMD3 of waveguide UTC photodiodes are characterized using a three-tone technique that is independent of harmonics from the optical sources. At 1 GHz, an OIP3 of 46.2 dBm at 60 mA of photocurrent is measured.

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.

Highly linear integrated coherent receivers for microwave photonic links

A coherent receiver with feedback was developed to linearly demodulate the phase of an analog signal. The receiver demonstrates a spur-free dynamic range of 125 dBmiddotPHz2/3 at a signal frequency of 300 MHz.

A high power Ge n-i-p waveguide photodetector on silicon-on-insulator substrate

We demonstrate high current operation of an evanescently coupled Ge waveguide photodetector grown on top of a Si rib waveguide. A 7.4μηι × 500μηι photodetector was found to dissipate 1.003 W of power (125.49mA at −8V).

Microwave characteristics of Ge n-i-p waveguide photodetectors on silicon-on-insulator substrate

We present microwave characteristics of evanescently coupled Ge waveguide photodetectors grown on Si rib waveguides. At 1 GHz and 40 mA of photocurrent, an OIP3 of 36.49 dBm is measured. Additionally, the maximum RF power extracted at 1 GHz is 14.35 dBm at 60 mA of photocurrent and 8 V reverse bias.

Linear phase demodulation using an integrated coherent receiver with an ultra-compact grating beam splitter

With phase modulation, it is possible to realize high dynamic range analog optical links, provided the transmitted radio frequency (RF) signal can be linearly demodulated. The linearity of traditional interferometer-based phase demodulators, however, is often limited by their sinusoidal response. To achieve high linearity, negative feedback is introduced to suppress non-linearities arising from the phase demodulation process [1]. High feedback gain reduces the net phase swing across the demodulator such that it operates within the linear regime. Additionally, both the signal and the noise are reduced by the same feedback factor, so there is no penalty in signal-to-noise ratio (SNR) [1]. The challenge is to make a receiver incorporating feedback that is operable at high frequencies. Because high loop gain as well as a wide bandwidth is required for efficient phase tracking, the physical delay in the feedback path must be kept sufficiently short in order to prevent the loop from oscillating. Previously, we have demonstrated an ultra-compact grating-based beam splitter [2], which divides the incoming optical beams in a region, over 30 times shorter than a conventional surface-ridge Multimode Interference (MMI) beam splitter. This key feature leads to a significant reduction in loop delay.

Dynamic Characterization of Distortion in Hybrid Silicon Evanescent Phase Modulators

We report the dynamic distortion of hybrid silicon phase modulators for three types of active layers. The third-order intermodulation distortion for each modulator was measured under various bias conditions by means of a two-tone technique. A peak phase input intercept point of 2.6pi for doped quantum-well modulators was achieved at a reverse bias of 4 V and a signal frequency of around 500 MHz.

Dynamic distortion characteristics of silicon evanescent detectors and phase modulators

The linearity of silicon evanescent modulators and quantum well detectors was measured for the first time. An output IP3 of 21 dBm for detectors and a peak phase input IP3 of 2.6pi for reverse biased phase modulators was achieved at 500 MHz.