Optimal design of 32 channels spectrum slicing WDM for optical fiber access network system

In this article, the spectrum sliced dense wavelength division multiplexed passive optical network (SS-DWDM–PON) has been investigated as a power efficient and cost effective solution for optical access networks. In this work an AWG demultiplexer is used to operate as slicing system. The high speed SS-DWDM system has been realized and investigated for 32 channels with data rate up to 3 Gb/s using broadband ASE source (LED). The 3 Gb/s signals both non-return-to-zero (NRZ) and return-to-zero (RZ) were demonstrated in 40 km optical fiber link with BER < 10⁻¹². The results obtained here demonstrate that SS-DWDM is well suited for Fiber-to-the-Home (FTTH) network.     

Performance enhanced down-stream signalling for next generation long-reach 10 Gbit/s passive optical networks

In this paper, we have analyzed the signal processing methods both in digital and optical domain to enhance the transmission performance of downstream signalling in long reach passive optical networks (LR-PONs). The impact of non-linear (NL) equalization through signal processing, i.e. Volterra Equalization (VE), Digital Backpropagation (BP) and Optical Phase Conjugation with Non-linearity Module (OPC-NM) is investigated, in 10 Gbit/s (XG) DP-QPSK long-reach wavelength division multiplexed (WDM) PONs without midspan repeaters over 120 km standard single mode fibre (SMF) link for down-stream signals. Due to the compensation of optical Kerr effects, the sensitivity penalty is reduced to 2 dB by BP algorithm, 1.5 dB by VE algorithm and 2.69 dB by OPC-NM. Moreover, with the implementation of NL equalization technique we are able to get the transmission distance of 126.6 km SMF for the 1:1024 split-ratio at 5 GHz channel spacing in the non-linear region. Furthermore, the concept of super passive optical network (S-PON) is also evaluated, which involves a repeater stage consisting of optical amplifiers, to study the feasibility for receiver side signal processing and simplification.     

Flexible broadcasting and multicasting in 4λ × 10 Gb/s AOPR TWDM PON system

In this letter, we propose a new architecture of Time Wavelength Division Multiplexing Passive Optical Network (TWDM PON) system to support dynamic multi wavelength allocation (DMWA) in both upstream and downstream directions using an integrated semiconductor optical amplifier (SOA) and arrayed waveguide grating (AWG) with multi wavelength select continuous wave (CW) pump probe signal module. The significance of this architecture is the flexible routing function with the capability of multicasting and broadcasting between multiple optical line terminal (OLT) PON port with multiple optical distribution network (ODN) link using a new wavelength tuning free (WTF) OLT transmitter module to eliminate wavelength tuning delay in downstream signal utilizing multicasting Cross Gain Modulation (XGM) wavelength conversion. The experimental results show that 4λ × 10-Gb/s TWDM PON system can be used to connect 4096 users with the conventional fixed wavelength OLT transceivers with 36 dB link loss.     

Realization of optoelectronic integrated transmitter and receiver for POF Applications

The optoelectronic integrated transmitter and receiver for 650 nm plastic optical fiber (POF) communication applications realized in 0.5 μm BCD (Biplor, CMOS and DMOS) process is first described in this paper. The 650 nm resonant cavity light emitting diode (RCLED) is used as light source. It is first proposed for optoelectronic integration of the transmitter by bonding RCLED to the driver chip. Temperature compensation technology is employed in the driver circuit to compensate for the modulation current. In the monolithic optoelectronic integrated receiver, large area multi-finger PIN photodetector (PD) that is compatible with standard IC process, transimpedance amplifier and post amplifier are presented. Measurement results show that the responsivity and capacitance of PD is 0.25 A/W and 5 pF, respectively. The sensitivity of receiver is −14.6 dBm at 180 Mb/s and BER is less than 10⁻⁹ for 650 nm input light by POF. A clear eye diagram is demonstrated for 180 Mb/s PRBS. These indicate that optoelectronic integrated chips can be employed in high-speed POF-based Fast Ethernet systems for broadband access network applications.     

Hybrid buffering architecture for packet contention resolution of an optical packet switch

Packet contention is a major issue in optical packet switching network and it is not a trivial task to resolve due to lack of optical RAM technology. In order to resolve contention optical buffering approach is used using fiber delay lines (FDLs). Yet there is a heavy packet loss rate due to unavailability of output port and free FDLs. This paper proposes a hybrid buffering architecture using feed-forward and feedback shared FLDs to resolve packet contention resolution of an optical packet switch. Feed-forward FDLs are used as primary buffer and feedback FDLs are implemented as supplementary buffer. Simulation result shows that proposed hybrid buffering switch achieves packet loss rate between 10⁻¹ and 10⁻² at heavy traffic load (ρ = 0.9) for a 32 × 32 switch using different FDL length.     

Research on OCDMA-based PON monitoring technologies

An optical fiber fault location method based on OCDMA coding is proposed, which may locate branch optical fiber fault at local side. The method expands dynamic range through coding gain without influencing event distinction degree. Through simulation, it indicates that dynamic range of the method may support optical fiber fault detection in PON with branching ratio of 1:16 and transmission distance of 20 km, while the distinction degree is about 10 cm.     

Splitting-on-demand optical power splitters using multimode interference (MMI) waveguide with programmed modulations

Reconfigurable multi-channel optical power splitter is proposed and its optical properties are calculated. The device can dynamically reconfigure the number of splitting channels by providing programmed refractive index modulations on a multimode interference (MMI) waveguide. A reconfigurable 3-channel optical power splitter is designed to work as 1 × 1, 1 × 2 or 1 × 3 optical power splitter depending on the state of the heat electrodes using thermo-optic modulation, and the input light can be distributed to three output channels with sequential orders. The device can work in the whole C-band (1530-1565 nm) with extinction ratio better than −29.0 dB, excess loss better than −0.45 dB, imbalance better than 0.08 dB and polarization dependent loss (PDL) better than 0.14 dB. The design conception is scalable to a multi-channel splitting-on-demand optical power splitter which can divide input light to 1, 2, …, N output channels equally by using the 3-channel reconfigurable optical power splitter as a building block.     

Optical implementation of (3, 3, 2) regular rectangular CC-Banyan optical network

CC-Banyan network plays an important role in the optical interconnection network. Based on previous reports of (2, 2, 3) the CC-Banyan network, another rectangular-Banyan network, i.e. (3, 3, 2) rectangular CC-Banyan network, has been discussed. First, according to its construction principle, the topological graph and the routing rule of (3, 3, 2) rectangular CC-Banyan network have been proposed. Then, the optically experimental setup of (3, 3, 2) rectangular CC-Banyan network has been designed and achieved. Each stage of node switch consists of phase spatial light modulator (PSLM) and polarizing beam-splitter (PBS), and fiber has been used to perform connection between adjacent stages. PBS features that s-component (perpendicular to the incident plane) of the incident light beam is reflected, and p-component (parallel to the incident plane) passes through it. According to switching logic, under the control of external electrical signals, PSLM functions to control routing paths of the signal beams, i.e. the polarization of each optical signal is rotated or not rotated 90° by a programmable PSLM. Finally, the discussion and analysis show that the experimental setup designed here can realize many functions such as optical signal switch and permutation. It has advantages of large number of input/output-ports, compact in structure, and low energy loss. Hence, the experimental setup can be used in optical communication and optical information processing.     

Investigation of a high-speed optical FSK scheme for WDM-PON applications with centralized lightwave source

This paper proposes and numerically investigates a novel high-speed wavelength-division-multiplexed passive optical network (WDM-PON) architecture with colorless user terminals based on the use of orthogonal modulation scheme for downstream and upstream transmission. The 40 Gb/s optical frequency shift keyed (FSK) downstream data is generated based on carrier-suppressed modulation. At optical network unit, the downstream signal is directly re-modulated by the 2.5 Gb/s up-stream data and sent back with the same fiber. Error free transmission over 20 km single mode fiber can be observed for both downstream and upstream signals in our simulation. Power budget, tolerance of channel spacing, FSK tone spacing and dispersion are all investigated. Factors that might influence the stability of the system are analyzed and an extended hybrid wired/wireless version of the scheme is also given.     

Optical power equalization for upstream traffic with injection-locked Fabry-Perot lasers in TDM-PON

An optical power equalization of upstream traffic in time-division-multiplexed passive optical network (TDM-PON) based on injection-locked Fabry-Perot lasers has been experimentally investigated. The upstream transmitters with stable spectrum are achieved by using an external injection light source in the optical line terminal (OLT). The different upstream powers can be equalized by injection locking a Fabry-Perot laser diode (FP-LD) biased below threshold current in OLT. The dynamic upstream power range from − 8.5 to − 19.5 db m is reduced to a 1.6 dB maximal power variation, when the uplink signal is directly modulated at 1.25 Gb/s.     

A novel full duplex 16 Gbps SCM/ASK radio over fiber WDM-PON sharing wavelength for up- and down-link using bidirectional reflective filter

In this paper, a new bidirectional wavelength division multiplexing radio-over-fiber (WDM-RoF) using Subcarrier Multiplexing/Amplitude Shift Keying (SCM/ASK) is proposed which shares the same wavelengths for both up-link and down-link. A bidirectional reflective filter (BRF) is utilized in the upstream link to provide a reliable bidirectional optical channel. WDM is used to further increase the capacity of system. Simulation of the proposed scheme demonstrates 1 Gbps down- and up-link data stream for 16 channels over the length of 25 km with acceptable Q-factor (>6 dB).     

Giga-bit optical receiver for plastic optical fibre

An optical receiver with high sensitivity and linearity specially designed for Giga-bit communications over small-bandwidth high-attenuation multimode plastic optical fiber is presented. An automatic gain control transimpedance amplifier and linear post amplifiers are used to maintain a good performance with multilevel modulation. Using multilevel signaling and large-diameter integrated photodiodes make the presented optical receiver suitable for large core plastic optical fiber. For a wavelength of 675 nm, a sensitivity of −26.3 dB m (BER = 10⁻⁹) at 500 Mb/s is presented by a binary signal. A data rate of 1 Gb/s and a sensitivity of −19.8 dB m (BER = 10⁻⁹) are achieved with four-level pulse amplitude modulation.     

BLS polarization-induced performance degradation in WDM-PON systems based on wavelength-locked FP-LDs

We experimentally investigated the performance degradation due to broadband light source (BLS) polarization in wavelength-division multiplexing-passive optical network systems based on a wavelength-locked Fabry-Perot laser diode. The results showed that the BLS polarization difference between two polarization states should be less than 3 dB, and its injection power should be greater than −18 dBm for a received-power penalty of less than 1 dB.     

Bidirectional WDM-PON architecture using a reflective filter and cyclic AWG

We proposed and demonstrated a bidirectional SCM-WDM PON using a reflective filter and cyclic AWG where up/downlink data could be provided using a single optical source. In the proposed scheme, the signal for downstream was modulated by a single CW laser diode and remodulated in the optical network unit as an upstream, the proposed WDM-PON scheme can offer the SCM signal for broadcasting service. In this paper, 1 Gb/s signals both for up- and downstream were demonstrated in 10 km bidirectional optical fiber link.     

Performance improvement and wavelength reuse in millimeter-wave radio-over-fiber links incorporating all-fiber optical interleaver

Simultaneous downlink performance improvement and uplink wavelength reuse in a full-duplex millimeter-wave (MMW) radio-over-fiber (RoF) system by using a simple and cost-effective all-fiber optical interleaver are proposed and demonstrated. The MMW RoF downlink performance improvement is based on suppressing optical carrier-to-sideband ratio (OCSR), with which the mechanism is confirmed by theoretic analysis and derived experimental results. Measured results show that, by suppressing OCSR using a fabricated all-fiber optical interleaver, the downlink optical receiver sensitivity is improved about 2.1 dB. The downlink data rate is 1.25 Gbit/s and the carrier frequency is 58.1 GHz; the link consists of 6 km optical single-mode fiber and 1 m wireless connection. On the other hand, with the interleaver suppressing downlink OCSR, simultaneously an optical carrier is recovered from the RoF downlink and is reused for RoF uplink transmission. The uplink is operated at 62.9 GHz and the data rate is the same 1.25 Gbit/s. With the recovered optical carrier, a laser-free remote access point is achieved. The principle, structure, and fabrication of an all-fiber optical interleaver are also presented in this paper.     

Transmission of 4× 40/10 Gbps in a WDM-PON using NRZ-DQPSK/ASK modulation

In this paper we demonstrate the feasibility to deploy a wavelength division multiplexing passive optical network (WDM-PON) of a 30 km standard single-mode fiber (SSMF-28) carrying 160 Gbps data in downstream and 40 Gbps through the uplink. The developed method is based on the comparison between two WDM-PON systems of 4 channels with the same characteristics, using two different formats of modulation in OLTs. The first system uses the NRZ-ASK in the downlink direction, while the second uses the NRZ-DQPSK.     

10 Gb/s TDM passive optical networks using four wavelengths multiplexed channels

We propose a new architecture for 10 Gb/s upstream traffic in TDM-PON using externally injection-locked Fabry-Perot laser diodes (FP-LDs) in each optical network unit (ONU). Four directly modulated 2.5 Gb/s FP-LDs were injection-locked by continuous wave (CW) carriers distributed from the optical line terminal (OLT). Hence, a total of 10 Gb/s upstream traffic can be achieved. Experimental results show negligible power penalty at a transmission of 25 km standard single mode fiber (SMF) without dispersion compensation. The performance of the injection-locked FP-LD is also studied.     

χ measurement and optical limiting studies of urea picrate

The molecular charge complex urea picrate (UP) was synthesized and its third order nonlinear optical properties have been investigated using a single beam Z-scan technique with nanosecond laser pulses at 532 nm. Open aperture data of the compound indicates two photon absorption at this wavelength. The nonlinear refractive index n₂, nonlinear absorption coefficient β, magnitude of effective third order susceptibility χ⁽³⁾, the second order hyperpolarizability γ_h and the coupling factor ρ have been estimated. The experimentally determined values of β, n₂, Re χ⁽³⁾ and Im χ⁽³⁾, γ_h and ρ of the compound UP are 2.146 cm/GW, −1.258×10⁻¹¹ esu, −1.347×10⁻¹³ esu, 0.377×10⁻¹³ esu, 0.69×10⁻³² esu and 0.28, respectively. The compound exhibits good optical limiting at 532 nm with the limiting threshold of 80 μJ/pulse. Our studies suggest that compound UP is a potential candidate for optical device applications such as optical limiters.     

Utilization of four WDM channels with signal remodulation of OFDM-QAM for 10 Gb/s uplink passive optical networks

In this investigation, we experimentally investigate an extended reach (ER) time-division-multiplexed passive optical network (TDM-PON) using four wavelength-multiplexed channels to achieve 16 Gb/s downlink and 10 Gb/s uplink traffic. Each downlink signal uses the highly spectral efficient 4 Gb/s OFDM-QAM, and each uplink signal is generated by signal remodulating the downlink signal via a reflective semiconductor amplifier (RSOA) at 2.5 Gb/s non-return-to-zero (NRZ). In addition, the performance of the proposed ER TDM-PON has also been analyzed and discussed.     

Preparation of ZnO-doped Al films by spray pyrolysis technique

Al-doped zinc oxide (AZO) thin films have been prepared by spray pyrolysis (SP) technique of zinc acetate and aluminium nitrate, and the effect of thickness on structural and optical properties has been investigated. The structural and optical characteristics of the AZO films were examined by X-ray diffraction (XRD) and double-beam spectrophotometry. These films, deposited on glass substrates at an optimal substrate temperature (T_S = 450 °C), have a polycrystalline texture with a hexagonal structure. Transmission measurements showed that for visible wavelengths, the AZO films have an average transmission of over 90%. The optical parameters have been calculated. The dependence of the refractive index, n, and extinction coefficient, k, on the wavelength for the sprayed films is also reported. Optical band gap of AZO is 3.30 and 3.55 eV, respectively, depending on the film thicknesses.