Silicon-based large-scale photonic integrated circuits are becoming important, due to the need for higher complexity and lower cost for optical transmitters, receivers and optical buffers. In this paper, passive technologies for large-scale photonic integrated circuits are described, including polarization handling, light non-reciprocity and loss reduction. The design rule for polarization beam splitters based on asymmetrical directional couplers is summarized and several novel designs for ultra-short polarization beam splitters are reviewed. A novel concept for realizing a polarization splitter–rotator is presented with a very simple fabrication process. Realization of silicon-based light non-reciprocity devices (e.g., optical isolator), which is very important for transmitters to avoid sensitivity to reflections, is also demonstrated with the help of magneto-optical material by the bonding technology. Low-loss waveguides are another important technology for large-scale photonic integrated circuits. Ultra-low loss optical waveguides are achieved by designing a Si3N4 core with a very high aspect ratio. The loss is reduced further to <0.1 dB m−1 with an improved fabrication process incorporating a high-quality thermal oxide upper cladding by means of wafer bonding. With the developed ultra-low loss Si3N4 optical waveguides, some devices are also demonstrated, including ultra-high-Q ring resonators, low-loss arrayed-waveguide grating (de)multiplexers, and high-extinction-ratio polarizers. Newly developed photonic components could allow large-scale photonic integrated circuits to be built on silicon substrates. Daoxin Dai from Zhejiang University, China, alongside co-workers from the University of California, USA, have proposed several new optical technologies for use in photonic integrated circuits, which substitute or work alongside electrical circuits in optical devices. The researchers have designed new ultrashort polarization-handling devices that split high-intensity beams of light, and a ring optical isolator that reduces reflections. The team have also created a new waveguide based on silicon nitride that can guide optical waves with a minimal loss of energy. These new technologies will allow scientists to construct higher performance, more compact optical devices.

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Passive technologies for future large-scale photonic integrated circuits on silicon: polarization handling, light non-reciprocity and loss reduction

A novel ultra-short polarization beam splitter (PBS) based on a bent directional coupler is proposed by utilizing the evanescent coupling between two bent optical waveguides with different core widths. For the bent directional coupler, there is a significant phase-mismatch for TE polarization while the phase-matching condition is satisfied for TM polarization. Therefore, the TM polarized light can be coupled from the narrow input waveguide to the adjacent wide waveguide while the TE polarization goes through the coupling region without significant coupling. An ultra-short ( 10dB.

Novel ultra-short and ultra-broadband polarization beam splitter based on a bent directional coupler.

An ultrashort polarization beam splitter (PBS) based on an asymmetrical directional coupler is proposed by utilizing the evanescent coupling between a strip-nanowire and a nanoslot waveguide. In order to be convenient for integration with other components, mode converters between the nanoslot waveguide and the strip-nanowire are introduced and merged into S-bends to achieve an ultracompact PBS. As an example a 6.9 μm long PBS based on a silicon-on-insulator platform is designed, and the length of the coupling region is as small as 1.3 μm. Numerical simulations show that the present PBS has a very broad band (>160 nm) for an extinction ratio of >10 dB.

Ultrashort broadband polarization beam splitter based on an asymmetrical directional coupler.

In this paper, the basic principle of operation, design issues, limitations, recent developments and emerging research trends on wide-bandwidth lasers and modulators for radio-frequency photonic applications are reviewed. The topics covered are wide-bandwidth lasers, lumped and traveling-wave electroabsorption modulators, traveling-wave LiNbO/sub 3/, GaAs, and polymer modulators.

Wide-bandwidth lasers and modulators for RF photonics

Integrating the input and output waveguides with a multiple-quantum-well (MQW) electro-absorption (EA) optical modulator is shown to achieve ultra-high-speed modulation while keeping the total device length long enough for easy fabrication and packaging. Testing with fabricated modulators showed that a shorter modulation region results in a larger modulation bandwidth. The additional loss due to the waveguide integration was less than 1 dB. An optimized modulator showed a large modulation bandwidth of 50 GHz, a low driving voltage of less than 3 V, and a low insertion loss of 8 dB. A prototype module of this modulator had a bandwidth of greater than 40 GHz. Optimizing the MQW structure makes the modulator insensitive to polarization. These results demonstrate that MQW-EA modulators with integrated waveguides are advantageous in terms of fabrication, packaging, and ultra-high-speed modulation.

Ultra-high-speed multiple-quantum-well electro-absorption optical modulators with integrated waveguides

The authors have fabricated a ridge waveguide electroabsorption modulator based on the quantum-confined Stark effect in InGaAsP/InGaAsP multiple quantum wells. The drive voltage for 12-dB extinction ratio is 1.2 V, and the frequency response is flat within 2 dB from DC to 20 GHz. Operation at 20 Gb/s is reported. Extensive data concerning the parasitic phase modulation (chirping) are obtained as a function of applied bias acid operating wavelength. >

20 Gbit/s operation of a high-efficiency InGaAsP/InGaAsP MQW electroabsorption modulator with 1.2-V drive voltage

Polarization splitting in a directional coupler is realized for the first time in InP by using modal birefringence of the waveguide. The measured crosstalks at 1.52 mu m are, respectively, -16 dB and -17 dB for TE and TM modes. The device propagation loss is >

Polarization splitter based on modal birefringence in InP/InGaAsP optical waveguides

A multiplexer/demultiplexer based on a meander-type InP grating-assisted codirectional coupler is reported It provides simultaneous bidirectional operation at two different wavelengths within the same 13 /spl mu/m window, as well as high bit rate distribution at 15 /spl mu/m The same demultiplexer is usable in both optical terminals of a 13/sup +/ or 13/sup -//15 /spl mu/m access network

Three-waveguide two-grating codirectional coupler for 1.3-/1.3+/1.5 [micro sign]m demultiplexing in transceiver

The design and realisation on InP of a meander-type grating-assisted codirectional coupler optical filter exhibiting a 40 nm box-like spectral response with high sidelobe suppression and reduced anisotropy is reported. A thermal tuning range larger than 20 nm is electrically realised.

Tunable filter with box-like spectral response for 1.28/1.32 [micro sign]m duplexer application

We investigate the use of a multi-quantum well optical amplifier with tilted tapered waveguides and window structure for wavelength conversion in the 1.55 /spl mu/m range at up to 5 Gbit/s. A clear polarization independent regeneration is observed for wavelength down conversion over more than 30 nm and over a wide dynamic range of input extinction ratio.

http://ieeexplore.ieee.org/iel4/5806/15507/00715465.pdf

A. Carenco

Papers

20 Gbit/s operation of a high-efficiency InGaAsP/InGaAsP MQW electroabsorption modulator with 1.2-V drive voltage

Polarization splitter based on modal birefringence in InP/InGaAsP optical waveguides

Three-waveguide two-grating codirectional coupler for 1.3-/1.3+/1.5 [micro sign]m demultiplexing in transceiver

Tunable filter with box-like spectral response for 1.28/1.32 [micro sign]m duplexer application

Polarization insensitive wavelength conversion by cross gain modulation in a strained MQW optical amplifier