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).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.

3 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 . 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.

4 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., 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.

5 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. 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.

6 3. In this typeof module, a TO-CAN type LD and photodiode (PD)are attached to a cubic body. 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.

7 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. Outer shape and internal structure of the Micro -BOSAF igure 6 shows a schematic diagram of the Micro -BOSA chip.

8 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. 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 )

9 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. An LD coupling efficiency is designed to be 30% forthis Micro -BOSA, but a coupling efficiency higherthan 50% can be achieved. The Si microlens can beplaced precisely on a V-groove fabricated by orienta-tion-dependent etching on the SiOB because theouter shape of Si microlens is also precise. The outershape is fabricated Using MEMS 8 shows a cut model of the Micro -BOSA chip is attached to the ledge of astem. Electric pads and pins are connected by goldwires and hermetically sealed by a cap with a balllens.

10 Finally, an SC receptacle is aligned and attachedby YAG welding. The outer shape just looks like aTransmitter OSA (TOSA) or a Receiver OSA (ROSA),but in this case, Optical transmitting and receivingfunctions are incorporated in one OSA. In this Micro -BOSA, it is important to suppress across talk because an LD and a PD are packaged in asingle TO-CAN package. A TO-CAN cap with a balllens is designed whose inside surface is finished witha low-reflection coat. We also put a resin on the stemto absorb LD emission from a rear facet. With thesefeatures, an Optical cross talk is suppressed efficient-ly. To shutoff 1,550 nm or longer wavelength, anotheroptical filter is attached onto an SC receptacle facetnear the ball lens.