Silicon waveguide that converts polarization mode of light could speed up photonic circuits operation

Jun 09, 2011 By Lee Swee Heng
A schematic diagram of a combined polarization rotator and mode converter provides mode conversion to reduce propagation loss in the waveguide while retaining the original polarization state

Silicon is the dominant material for the fabrication of integrated circuits and is also becoming a popular material for making photonics circuits -- miniaturized circuits that use light instead of electronic signals for processing information. One of the challenges in the field, however, has been silicon’s intrinsic sensitivity to the polarization of light, which can limit the rate of information transmission. Jing Zhang, Tsung-Yang Liow and co-workers at the A*STAR Institute of Microelectronics have now developed a novel solution to this problem.

Light of different polarizations, which normally travel at the same speed in air, travel at different speeds in silicon waveguides due to random imperfections and asymmetries in the itself. To overcome this problem, the researchers turned to a scheme known as ‘ diversity’, by which incoming is split into two perpendicular modes of polarization, called the transverse electric (TE) and transverse magnetic (TM) modes. They then rotated the TM mode by 90° so that both of the modes propagate in parallel at the same speed inside the photonic circuit.

Zhang, Liow and their co-workers had previously demonstrated a silicon-based device, called a polarization rotator, which comprises the first half of the diversity scheme (see image). The rotator transforms TM light into TE light by passing the light through a horizontal and then rotating it into a vertical waveguide. In their present work, they designed, built and characterized a device that completes the second half of the scheme. Called a polarization mode converter, it transforms TE light in the vertical waveguide into TE light in a horizontal waveguide. By connecting their mode converter to their rotator, the researchers were able to construct a polarization diversity scheme that provides mode conversion to reduce propagation loss in the waveguide while retaining the original polarization state.

Both halves of the polarization rotation device work by gradually changing the geometry of the waveguide, which in turn changes the polarization mode of the light it is guiding. The Singapore research team characterized their devices by studying the signal loss introduced over the transition length between polarization modes, as well as the propagation loss in the rest of the device. They found that the device efficiencies would need to be improved to be practical, for example by reducing the roughness of the waveguide walls through thermal oxidation, and by improving the coupling between the waveguide and the fiber optic cable connected to it.

Explore further: High power laser sources at exotic wavelengths

More information: Zhang, J., et al. Silicon waveguide based TE mode converter. Optics Express 18, 25264–25270 (2010).

Provided by Agency for Science, Technology and Research (A*STAR)

not rated yet
add to favorites email to friend print save as pdf

Related Stories

Topological light: Living on the edge

Oct 21, 2013

( —Topology—the understanding of how things are connected—remains abstract, even with the popular example of doughnuts and coffee cups. This concept, esoteric as it appears, is also neat because ...

New level for continuous-wave terahertz lasers

Oct 03, 2013

Since the first quantum cascade (QC) laser was demonstrated in 1994 and implemented in THz regime in 2002, they have become one of the most important solid state light sources in this frequency range. The ...

Researchers steer light in new directions

Sep 16, 2013

A team of researchers led by San Francisco State University's Weining Man is the first to build and demonstrate the ability of two-dimensional disordered photonic band gap material, designed to be a platform ...

Caltech engineers invent light-focusing device

Dec 07, 2012

(—As technology advances, it tends to shrink. From cell phones to laptops—powered by increasingly faster and tinier processors—everything is getting thinner and sleeker. And now light beams ...

Lenses can bend light and sound in almost any direction

Apr 02, 2012

( -- When an optical fiber is bent by 90° or more, the light begins to leak away, posing a problem for fiber optics communications. But by using special lenses that can bend light by not only ...

Recommended for you

Robotics goes micro-scale

16 hours ago

( —The development of light-driven 'micro-robots' that can autonomously investigate and manipulate the nano-scale environment in a microscope comes a step closer, thanks to new research from the ...

High power laser sources at exotic wavelengths

Apr 14, 2014

High power laser sources at exotic wavelengths may be a step closer as researchers in China report a fibre optic parametric oscillator with record breaking efficiency. The research team believe this could ...

Combs of light accelerate communication

Apr 14, 2014

Miniaturized optical frequency comb sources allow for transmission of data streams of several terabits per second over hundreds of kilometers – this has now been demonstrated by researchers of Karlsruhe ...

User comments : 0

More news stories

Better thermal-imaging lens from waste sulfur

Sulfur left over from refining fossil fuels can be transformed into cheap, lightweight, plastic lenses for infrared devices, including night-vision goggles, a University of Arizona-led international team ...

Robotics goes micro-scale

( —The development of light-driven 'micro-robots' that can autonomously investigate and manipulate the nano-scale environment in a microscope comes a step closer, thanks to new research from the ...

Hackathon team's GoogolPlex gives Siri extra powers

( —Four freshmen at the University of Pennsylvania have taken Apple's personal assistant Siri to behave as a graduate-level executive assistant which, when asked, is capable of adjusting the temperature ...

Deadly human pathogen Cryptococcus fully sequenced

Within each strand of DNA lies the blueprint for building an organism, along with the keys to its evolution and survival. These genetic instructions can give valuable insight into why pathogens like Cryptococcus ne ...