An overview of analog microwave photonics will be presented. The performance requirements for externally-modulated analog microwave photonic links will be reviewed with specific emphasis placed on modulator efficiency, laser noise, detected photocurrent, and link linearity.

http://ieeexplore.ieee.org/iel5/6387506/6403300/06403360.pdf

Microwave photonics

Dual-comb spectroscopy is an emerging new spectroscopic tool that exploits the frequency resolution, frequency accuracy, broad bandwidth, and brightness of frequency combs for ultrahigh-resolution, high-sensitivity broadband spectroscopy. By using two coherent frequency combs, dual-comb spectroscopy allows a sample’s spectral response to be measured on a comb tooth-by-tooth basis rapidly and without the size constraints or instrument response limitations of conventional spectrometers. This review describes dual-comb spectroscopy and summarizes the current state of the art. As frequency comb technology progresses, dual-comb spectroscopy will continue to mature and could surpass conventional broadband spectroscopy for a wide range of laboratory and field applications.

Dual-comb spectroscopy

Researchers demonstrate a microwave generator based on a high-Q optical resonator and a frequency comb functioning as an optical-to-microwave divider. They generate 10 GHz electrical signals with a fractional frequency instability of ≤8 × 10−16 at 1 s.

/pdf/generation-of-ultrastable-microwaves-via-optical-frequency-4zkqlu6ady.pdf

Generation of ultrastable microwaves via optical frequency division

Ultraviolet (UV) photodetectors have drawn extensive attention owing to their applications in industrial, environmental and even biological fields. Compared to UV-enhanced Si photodetectors, a new generation of wide bandgap semiconductors, such as (Al, In) GaN, diamond, and SiC, have the advantages of high responsivity, high thermal stability, robust radiation hardness and high response speed. On the other hand, one-dimensional (1D) nanostructure semiconductors with a wide bandgap, such as β-Ga2O3, GaN, ZnO, or other metal-oxide nanostructures, also show their potential for high-efficiency UV photodetection. In some cases such as flame detection, high-temperature thermally stable detectors with high performance are required. This article provides a comprehensive review on the state-of-the-art research activities in the UV photodetection field, including not only semiconductor thin films, but also 1D nanostructured materials, which are attracting more and more attention in the detection field. A special focus is given on the thermal stability of the developed devices, which is one of the key characteristics for the real applications.

A Comprehensive Review of Semiconductor Ultraviolet Photodetectors: From Thin Film to One-Dimensional Nanostructures

Light emitting diodes reliability review

The first sub-100nm technology that allows the monolithic integration of optical modulators and germanium photodetectors as features into a current 90nm base highperformance logic technology node is demonstrated. The resulting 90nm CMOS-integrated Nano-Photonics technology node is optimized for analog functionality to yield power-efficient single-die multichannel wavelength-mulitplexed 25Gbps transceivers.

https://researcher.watson.ibm.com/researcher/files/us-yvlasov/assefa_IEDM_final.pdf

A 90nm CMOS integrated Nano-Photonics technology for 25Gbps WDM optical communications applications

We demonstrate two modified uni-traveling carrier photodiode (MUTC) structures that incorporate a charge or “cliff” layer to attain high-saturation-current. MUTC1 achieved responsivity of 0.82 A/W and 134 mA saturation current at -6-V and 20 GHz. The MUTC2 structure, which has higher doping density in the cliff layer and thinner absorption region, exhibited a higher saturation current of 144 mA (at -5-V) and an improved 3 dB bandwidth of 24 GHz; however, the responsivity was reduced to 0.69 A/W. For MUTC2, a high-saturation-current bandwidth product of 3456 GHz mA has been achieved. An intermodulation distortion figure of merit, IP3, > dBm at 20 GHz was observed for both MUTC structures.

High-Saturation-Current Modified Uni-Traveling-Carrier Photodiode With Cliff Layer

We demonstrate a flip-chip bonded modified uni-traveling carrier (MUTC) photodiode with an RF output power of 0.75 W (28.8 dBm) at 15 GHz and OIP3 as high as 59 dBm. The photodiode has a responsivity of 0.7 A/W, 3-dB bandwidth > 15 GHz, and saturation photocurrent > 180 mA at 11 V reverse bias.

High-power high-linearity flip-chip bonded modified uni-traveling carrier photodiode

We demonstrate optical modulation rates exceeding the conventional cavity linewidth limit using a silicon coupling modulated microring. Small-signal measurements show coupling modulation was free of the parasitic cavity linewidth limitations at rates at least 6× the cavity linewidth. Eye diagram measurements show coupling modulation achieved data rates > 2× the rate attainable by conventional intracavity phase modulation. We propose to use DC-balanced encoding to mitigate the inter-symbol interference in coupling modulation. Analysis shows that coupling modulation can be more efficient than intracavity modulation for large output swings and high-Q resonators. Coupling modulation enables very high-Q resonant modulators to be simultaneously low-power and high-speed, features which are mutually incompatible in typical resonant modulators studied to date.

Coupling modulation of microrings at rates beyond the linewidth limit

The performance of a receiver based on a CMOS amplifier circuit designed with 90nm ground rules wire-bonded to a waveguide germanium photodetector is characterized at data rates up to 40Gbps. Both chips were fabricated through the IBM Silicon CMOS Integrated Nanophotonics process on specialty photonics-enabled SOI wafers. At the data rate of 28Gbps which is relevant to the new generation of optical interconnects, a sensitivity of −7.3dBm average optical power is demonstrated with 3.4pJ/bit power-efficiency and 0.6UI horizontal eye opening at a bit-error-rate of 10−12. The receiver operates error-free (bit-error-rate < 10−12) up to 40Gbps with optimized power supply settings demonstrating an energy efficiency of 1.4pJ/bit and 4pJ/bit at data rates of 32Gbps and 40Gbps, respectively, with an average optical power of −0.8dBm.

Huapu Pan

Papers

A 90nm CMOS integrated Nano-Photonics technology for 25Gbps WDM optical communications applications

High-Saturation-Current Modified Uni-Traveling-Carrier Photodiode With Cliff Layer

High-power high-linearity flip-chip bonded modified uni-traveling carrier photodiode

Coupling modulation of microrings at rates beyond the linewidth limit

High-speed receiver based on waveguide germanium photodetector wire-bonded to 90nm SOI CMOS amplifier