Huiyuan Liu

First Demonstration of Six-Mode PON Achieving a Record Gain of 4 dB in Upstream Transmission Loss Budget

The power budget and costs are the two primary concerns for access networks. A major challenge is to minimize upstream power combining loss to increase the power budget. Spatial modes multiplexing offers the possibility to minimize upstream combining loss without significant added costs. We demonstrate the first integrated six-mode passive optical network, utilizing spatial modes to eliminate upstream combining loss. A record 4-dB net gain in power budget was achieved by fusion splicing a photonic lantern with a FMF, in contrast to the traditional power combining scheme with a single-mode power combiner/splitter. BERs <;10-9 were obtained for all the six modes enabling Ethernet transmission using commercial GPON equipment. The packet loss of all six modal channels was tested for 12 h. Finally, we discuss some special issues of few-mode PON regarding its practical application.

Few-mode fibre-optic microwave photonic links

The fibre-optic microwave photonic link has become one of the basic building blocks for microwave photonics. Increasing the optical power at the receiver is the best way to improve all link performance metrics including gain, noise figure and dynamic range. Even though lasers can produce and photodetectors can receive optical powers on the order of a Watt or more, the power-handling capability of optical fibres is orders-of-magnitude lower. In this paper, we propose and demonstrate the use of few-mode fibres to bridge this power-handling gap, exploiting their unique features of small acousto-optic effective area, large effective areas of optical modes, as well as orthogonality and walk-off among spatial modes. Using specially designed few-mode fibres, we demonstrate order-of-magnitude improvements in link performances for single-channel and multiplexed transmission. This work represents the first step in few-mode microwave photonics. The spatial degrees of freedom can also offer other functionalities such as large, tunable delays based on modal dispersion and wavelength-independent lossless signal combining, which are indispensable in microwave photonics.

Reducing group delay spread using uniform long-period gratings

Despite the promise of an orders-of-magnitude increase in transmission capacity, practical implementation of mode-division multiplexing faces a number of challenges. The most important among them is the complexity of digital signal processing (DSP) for compensating mode crosstalk and modal dispersion. The most promising method proposed so far for reducing this DSP complexity is strong mode coupling. We propose and demonstrate, for the first time, a method of inducing strong mode coupling and reducing group delay spread using uniform long-period gratings (LPGs). Even though the LPGs have a fixed grating period, mode coupling is effective among all mode groups and over a broad wavelength range. Both insertion loss and mode-dependent loss can be significantly reduced by optimizing the index profile of and the number of modes supported by the fiber in which the LPG is applied.

3×10 Gb/s mode group-multiplexed transmission over a 20 km few-mode fiber using photonic lanterns

We experimentally demonstrate 3×10 Gb/s mode group-multiplexed transmission with direction detection in a step-index few-mode fiber over a record reach of 20 km, enabled by low crosstalk photonic lanterns as mode group (de)multiplexers.

Experimental demonstration of 5-mode PON achieving a net gain of 4 dB in upstream transmission loss budget

We demonstrate the first integrated 5-mode passive optical network, utilizing spatial modes to eliminate upstream combining loss. BERs of less than 10-9 were obtained for all 5 modes enabling Ethernet transmission using commercial GPON equipment without packet loss.

Analog fiber-optic links using high-order fiber modes

We demonstrate the first analog fiber-optic link using high-order modes in FMFs to improve SFDR and reduce WDM penalties due to fiber nonlinearities. An 8-dB SFDR improvement and a 15-dB nonlinear crosstalk suppression were achieved.