Low - Cost Optical Transceiver for PON Using Micro …

1 11 Fujikura Technical Review, 20071. Introduction Fiber-to-the-home (FTTH) system is becomingwidely used now. Passive Optical Network (PON)system will be commonly selected because of its cost-effectiveness. In the PON system, every subscriber isrequired to install an Optical Network Unit (ONU) athis/her home. Therefore, cost reduction of the ONUis essential. A major portion of the ONU cost comesfrom an Optical Transceiver , and, therefore, the costreduction of the Transceiver is most have developed a novel Transceiver and anOptical Sub-Assembly (OSA), the key element of atransceiver, for Gigabit Ethernet-PON1)(GE-PON),which operates at 1 Gbit/s data rate Using Ethernettechnology.

2 A newly developed compact and low-costBidirectional Optical Sub-Assembly (BOSA)2), calledmicro-BOSA, can make the Transceiver a small formfactor. The design of the Transceiver was also opti-mized for the Micro -BOSA, reducing its total cost. The development was a joint work betweenFujikura Ltd. and Oki Electric Industry Co., Ltd. Themembers of Oki Electric Industry took charge of theoptical design and internal structure of the Micro -BOSA3)under their Silicon microlens technologies4).

3 Optoelectronic Circuits & Systems R & D Center ofFujikura developed packaging and assembling ofmicro-BOSA and designed the Optical Outline of the PON systemFigure 1 shows the outline of the PON system thatis one of the FTTH systems. One Optical fiber from acentral office is divided by an Optical splitter on theway to subscribers. Multiple subscribers can there-Low - Cost Optical Transceiver for PON Using Micro -BOSAK oichiroMasuko1, KenjiNishide2, SusumuNakaya2, TeijiroOri2, OsamuKikuchi3, RyouSekikawa4and DaisukeShimura4A novel Micro -Bidirectional Optical Sub-Assembly (BOSA) has been developed in which opti-cal transmitting and receiving functions are incorporated in a single TO-CAN package.

4 A newcompact and cost-effective Passive Optical Network (PON) Optical Network Unit (ONU) trans-ceiver Using the Micro -BOSA has also been developed. Low-cost feature is achieved with a pas-sive alignment technology and a simplified integrated structure of the Micro -BOSA. Both elec-trical and Optical characteristics are sufficient to comply with Gigabit Ethernet (GE)-PONONU Transceiver specification. In this paper, the structure and characteristics of the transceiverare reported. Drop cableClosure with splittersAerial cableFeeder cable Central officeGE-PON OLTGE-PON OLTGE-PON PON Applied Electronics Technology Department of Optics and ElectronicsLaboratory2 Optoelectronic Circuits & Systems R & D Center 3 Optical Module R & D Department of Optoelectronic Circuits & Systems R &D Center4 Oki Electric Industry Co.

5 , driverBidirectional Optical Sub-Assembly(BOSA)DataBurstsignalDataSig naldetectRx circuit boardPD TO-CANO ptical fiber1,310nm1,490nm1,550nmPost amplifierPre-amplifierPDLDmPDWDMC onventional Transceiver for PON ONUTx circuit boardLD Block diagram of an ONU Optical share an Optical Line Terminal (OLT) in the cen-tral office. Figure 2 shows the block diagram of a con-ventional GE-PON ONU Transceiver . In this system,upstream signal is carried by a 1,310 nm wavelengthlight, and downstream signal is carried by a 1,490 nmwavelength light, so that a bidirectional communica-tion is realized by a single Optical fiber.

6 Burst trans-mitting function to operate laser diode (LD) only dur-ing a requested period is also required for the ONUsbecause they share one OLT. The function to shutoff a 1,550 nm signal is alsorequired because a video service on 1,550 nm isplanned in the Structure of the proposed Transceiver andthe Conventional transceiverConventional Transceiver generally uses a cubicoptical module shown as BOSA in Fig. 3. In this typeof module, a TO-CAN type LD and photodiode (PD)are attached to a cubic body.

7 A Wavelength DivisionMultiplexing (WDM) filter is fixed inside the body soas to make a 45 angle to the LD and PD Optical the module itself along with the circuit board ofthe Optical Transceiver becomes complicated. A pigtailfiber with an SC connector is usually attached to theBOSA. It results in high material and assemblingcost. Proposed Optical transceiverFigure 4 shows the appearance of the proposedoptical Transceiver . The Transceiver is designed tocomply with the Small Form Factor (SFF)Multisource Agreement (MSA) standard.

8 An SC-typeoptical connector is mated to one end of the transceiv-er. Upstream signal is carried by a 1,310 nm wave-length light, and downstream signal is carried by a1,490 nm wavelength light because the Transceiver isdesigned for GE-PON ONU. The transmission datarate is 5 shows the internal structure of the prod-uct. A cylindrical object on the left side is the Micro -BOSA and on the right side is a circuit board for theIC with an LD driver and a post amplifier for signalreceiving.

9 Outer shape and internal structure of the Micro -BOSAF igure 6 shows a schematic diagram of the Micro -BOSA chip. A silicon Optical bench (SiOB) with opti-cal devices, called Micro -BOSA chip, is fixed in themicro-BOSA. An LD, a PD, Si microlens, a WDM fil-ter, a transimpedance amplifier (TIA), and capacitorsare mounted on the SiOB with passive alignmenttechnologies. Upstream signal from an LD is collimat-ed by an Si microlens, goes through a WDM filter, iscondensed by a ball lens and coupled into an opticalfiber.

10 Downstream signal from the Optical fiber is col-limated by the ball lens, reflected by the WDM filter,condensed and bent a little downward by an Si12Tx circuit boardRx circuit boardBOSAO ptical Example of a conventional Outer shape of the proposed Optical Internal structure of the proposed Optical microlensPre-amplifierWDM filterUp-stream1,310nmDown-stream1,490nm Ball lensSi The Micro -BOSA , reflected by a mirror on SiOB and coupledinto a 7 shows the details of the Si microlens thatis a kind of diffractive )The lenses can be fabri-cated in wafer scale based on the conventional Si LSIfabrication technology so that the form can be con-trolled very precisely.