We experimentally demonstrate an innovative Ultra Dense Wavelength Division Multiplexing (UDWDM) Passive Optical Networks (PON) that implements the full λ-to-the-user concept in a filterless distribution network. Key element of the proposed system is a novel class of coherent transceivers, purposely developed with a non-conventional technical approach. Indeed, they are designed and realized to avoid D/A-A/D converter stages and Digital Signal Processing (DSP) in favor of simple analog processing so that they match system, cost and power consumption requirements of the access networks without sacrificing the overall performance. These coherent transceivers target different use case scenarios (residential, business, fixed, wireless) still keeping perfect compatibility and coexistence with legacy infrastructures installed to support gray, Time Division Multiplexed (TDM) PON systems. Moreover, the availability of coherent transceivers of different cost/performance ratios allows for deployments of different quality service grades. In this paper, we report the successful field trial of the proposed systems in a testbed where 14 UDWDM channels (and one legacy E-PON system) are transmitted simultaneously in a dark-fiber network deployed in the city of Pisa (Italy), delivering real-time and/or test traffic. The trial demonstrated filterless operations (each remote node selects individually its own UDWDM channel on a fine 6.25 GHz grid), real-time GbE transmissions (by using either fully analog or light digital signal processing), multirate transmission (1.25 and 10 Gb/s/), high Optical Distribution Network loss (18 ÷ 40 dB) as well as a bidirectional channel monitoring system.

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We experimentally demonstrate a simultaneous amplitude and phase modulation of a monolithically integrated dual electro-absorption modulated laser (DEML). The proposed technique combines a 4-ary direct phase modulation with a 2-level amplitude modulation obtaining an 8-ary amplitude-phase shift keying (8-APSK) external-modulator-free transmitter. Its performance was tested up to 7.5 Gb/s in a 25-km single mode fiber link with intradyne coherent detection. A receiver sensitivity of-42.5 dBm was achieved at FEC limit BER = 4x10-3. The results show that the proposed system can be an efficient flexible transmitter for next generation passive optical networks.

This paper describes a technique for calculating the resultant contrast of displays incorporating various filters or filter combinations. In particular, contrast of such displays employing red or green light emitting diodes (LED's) as the active elements is tabulated. The results indicate that adequate contrast enhancement of red LED's in high light level environments is usually achieved using neutral density or bandpass filters with antireflective coatings. Green LED'S must be designed to have a high degree of specular reflectance so that a circular polarizer may be employed in order to achieve similar results. A discussion of required filter bandwidth to accommodate shifts in peak spectral output of LED'S due to manufacturer's tolerances and temperature effects is also included.

A 15 dB differential link-loss ultra-dense wavelength division multiplexing passive optical network (UDWDM-PON) with two optical network units (ONU) spectrally spaced 6.25 GHz is experimentally implemented and tested. The ONU transmitters consist of direct phase modulated distributed feedback lasers (DFB) through a digital beat signal, whose amplitude and duty cycle are optimized for maximum phase variations, avoiding the need for an analogue equalizer. We achieved receiver sensitivities of-53 dBm,-50.5 dBm, and-45 dBm for bit rates of 1.25 Gb/s, 2.5 Gb/s, and 5 Gb/s respectively at BER = 4•10-3 with an intradyne coherent receiver.