Effective user accommodation will be more and more important in passive optical networks (PONs) in the next decade since the number of subscribers has been leveling off as well and it is becoming more difficult for network operators to keep sufficient numbers of maintenance workers. Drastically reducing the number of small-scale communication buildings while keeping the number of accommodated users is one of the most attractive solutions to meet this situation. To achieve this, we propose two types of long-reach repeater-free upstream transmission configurations for PON systems; (i) one utilizes a semiconductor optical amplifier (SOA) as a pre-amplifier and (ii) the other utilizes distributed Raman amplification (DRA) in addition to the SOA. Our simulations assuming 10G-EPON specifications and transmission experiments on a 10G-EPON prototype confirm that configuration (i) can add a 17km trunk fiber to a normal PON system with 10km access reach and 1 : 64 split (total 27km reach), while configuration (ii) can further expand the trunk fiber distance to 37km (total 47km reach). Network operators can select these configurations depending on their service areas.

We propose the cost-effective bit-level coarse wavelength division multiplexing (CWDM)-based power budget extender (PBEx) that can provide a high link budget of 54dB in a symmetric-rate 10-Gbit/s Ethernet passive optical network (10/10G-EPON). The proposed CWDM-based PBEx comprises a 2R-based 10/10G-EPON central office terminal (COT) and 3R-based 10/10G-EPON remote terminal (RT). It can apply several conventional CWDM technologies at the feeder fiber to reduce the amount of optical fiber required and increase the link capacity. Thus, it mainly conducts a wavelength conversion and signal retiming, as well as an upstream burst-mode for a continuous-mode conversion. We experimentally demonstrate the feasibility of a CWDM-based PBEx through packet-level testing using a pre-commercialized 10/10G-EPON system. We can confirm that the proposed solution can support a 128-way split at a distance of over 40km per CWDM channel with an enlarged loss budget of 54dB. We can also satisfy loss-free service during a packet transmission of 1010 both downstream and upstream.

The 10-gigabit Ethernet passive optical network (10G-EPON) is a promising candidate for the next generation of fiber-to-the-home access systems. In the symmetric 10G-EPON system, the gigabit Ethernet passive optical network (GE-PON) and 10G-EPON will have to co-exist on the same optical network. For this purpose, an optical triplexer (10G-transmitter, 1G-transmitter, and 10G/1G-receiver) for optical line terminal (OLT) transceivers in 10G/1G co-existing EPON systems has been developed. Reducing the size and cost of the optical triplexer has been one of the largest issues in the effort to deploy 10G-EPON systems for practical use. In this paper, we describe a novel small and low-cost dual-rate optical triplexer for use in 10G-EPON applications. By reducing the optical path length by means of a light collection system with a low-magnification long-focus coupling lens, we have successfully miniaturized the optical triplexer for use in 10G-EPON OLT 10-gigabit small form factor pluggable (XFP) transceivers and decreased the number of lenses. A low-cost design of sub-assemblies also contributes to cost reduction. The triplexer's performance complies with IEEE 802.3av specifications.

As a future passive optical network (PON) system, the 10 Gigabit Ethernet PON (10G-EPON) has been standardized in IEEE 802.3av. As conventional Gigabit Ethernet PON (GE-PON) systems have already been widely deployed, 1G/10G co-existence technologies are strongly required for the next system. A gated voltage-controlled-oscillator (G-VCO)-based 10-Gb/s burst-mode clock and data recovery (CDR) circuit is presented for a 1G/10G co-existence PON system. It employs two new circuits to improve jitter transfer and provide tolerance to 1G/10G operation. An injection-controlled jitter-reduction circuit reduces output-clock jitter by 7 dB from 200-MHz input data jitter while keeping a short lock time of 20 ns. A frequency-variation compensation circuit reduces frequency mismatch among the three VCOs on the chip and offers large tolerance to consecutive identical digits. With the compensation, the proposed CDR circuit can employ multi VCOs, which provide tolerance to the 1G/10G co-existence situation. It achieves error-free (bit-error rate < 10-12) operation for 10-G bursts following bursts of other rates, obviously including 1G bursts. It also provides tolerance to a 256-bit sequence without a transition in the data, which is more than enough tolerance for 65-bit CIDs in the 64B/66B code of 10 Gigabit Ethernet.

This paper reviews next generation optical access network standardization activities, focusing on 10-Gbps class TDM PON, and introduces key technologies for their co-existence with deployed systems.

This paper proposes a power saving mechanism with variable sleep period to reduce the power consumed by optical network units (ONUs) in passive optical network (PON) systems. In the PON systems based on time division multiplexing (TDM), sleep and periodic wake-up (SPW) control is an effective ONU power saving technique. However, the effectiveness of SPW control is fully realized only if the sleep period changes in accordance with the traffic conditions. This paper proposes an SPW control mechanism with variable sleep period. The proposed mechanism sets the sleep period according to traffic conditions, which greatly improves the power saving effect. In addition, the protocols needed between an optical line terminal (OLT) and ONUs are described on the assumption that the proposed mechanism is applied to 10 Gigabit (10G) class PON systems, i.e. IEEE 802.3av 10G-EPON and FSAN/ITU-T 10G-PON systems. The validity of the proposed mechanism is confirmed by numerical simulations.

We propose an optical switch control procedure for the Active Optical Access System (AOAS). Optical switches are used in AOAS instead of optical splitters in PON. In the proposed procedure, an OLT determines the switching schedules of optical switches on OSW (Optical Switching Unit) which is installed between OLT and ONU, and informs the OSW of them with a switch control frame preceding of data frame transmission. Then the switch controller on OSW controls the optical switches based on the switching schedules. We developed the prototype systems of OSW, OLT, and ONU. We implemented the optical switch control function with logic circuits on the prototype systems. We demonstrate the proposed procedure works effectively with logic circuits. We also evaluate the 10 Gps optical signal transmission between OLT and ONU. We demonstrate the receiver sensibility on OLT and ONU achieves the distance of 40 km for optical signals transmission with FEC (Forward Error Correction). These receivers are applicable for both AOAS and 10G-EPON.