A bidirectional grating serving both, as a polarization beam splitter and a vertical coupler for Silicon on Insulator
nanophotonic circuits is fabricated and characterized. The measured coupling efficiency is as high as 43%. The
demonstrated device has a large 3-dB bandwidth and a high extinction ratio between two orthogonal polarizations.
Electroabsorption modulators (EAM) based on quantum-confined Stark effect (QCSE) in multiplequantum
wells (MQW) have been demonstrated to provide high-speed, low drive voltage, and high
extinction ratio. They are compact in size and can be monolithically integrated with continuous-wave
(CW) lasers. In order to achieve both high speed and low drive-voltage operation, travelling-wave
(TW) electrode structures can be used for EAMs. The inherently low impedance of high-speed
EAMs may be transformed to values close to the standard 50Ohm impedance using periodic
microwave structures with a combination of passive transmission lines with high characteristic
impedance and active modulator sections with low impedance. Modulation bandwidths of 100GHz
(-3dBe) have been accomplished with electrical reflections lower than -10dB in a 50Ohm system.
Transmission at 80Gbit/s with non-return-to-zero (NRZ) code has been demonstrated for InP-based
TWEAMs using electronic time-domain multiplexing (ETDM), indicating the possibility of reaching
speeds of 100Gbit/s and beyond.
A packaged high speed reflective electroabsorption transceivers for radio-over-fiber applications is demonstrated. The transceiver, an AFPMD (Asymmetric vertically addressed Fabry-Perot Modulator/Detector), is successfully packaged into a standard module, originally intended for 10 Gbit/s Ethernet detectors. The packaging process and the electrical, optical and thermal performance of the packaged component are presented. A bandwidth of 6 GHz, a total reflective optical coupling loss of 7.1 dB and a responsitivity of 0.14 mA/mW are accomplished. By optimizing the operation optical wavelength and bias voltage, fifth-order nonlinearity dominates the intermodulation distortion and a spurious
free dynamic range (SFDR) of 101dB.Hz4/5 at 5.554GHz can be achieved experimentally.
Features such as large bandwidth, low drive voltage, compact size, and feasibility for monolithic laser integration make electro-absorption modulators (EAM) attractive candidates for ultra high-speed fiber-optical time division multiplexing (TDM). EAM with traveling-wave (TW) electrodes have successfully been demonstrated as a way to considerably increase the modulation bandwidth without sacrificing modulation efficiency. However, for reasonable modulation efficiency a low characteristic impedance (≈25Ω) has to be accepted. Termination with a matched load is necessary to benefit from the TW configuration. Thus, TWEAM with continuous impedance-matched transmission lines (TML) provide very high bandwidths, but suffer from high electrical return loss when using a 50Ω driver. A solution to this problem is to split up the modulator and insert passive TML segments between the active parts. The passive segments can be designed for a higher characteristic impedance than the active modulator parts with their inherently low impedance. In this way, the impedance seen at the electrical modulator input can be tailored for values that deliver optimum performance in combination with the available driving electronics (usually 50Ω). Only little bandwidth is sacrificed with the segmented design. Recently, we have demonstrated state-of-the-art performance of segmented TWEAM. These devices exhibit low electrical return loss (<-15dB) and a flat small signal modulation response in the characterized frequency range of 0.04 to 50GHz. 50Gb/s operation is demonstrated. An extinction of 10dB with 3Vp-p is achieved at 40Gb/s.