Transmitter Optical Subassembly Research Articles

Component Prototypes Towards a Low-Latency, Small-Form-Factor Optical Link for the ATLAS Liquid Argon Calorimeter Phase-I Trigger Upgrade

This paper presents several component prototypes towards a low-latency, small-form-factor optical link designed for the ATLAS Liquid Argon Calorimeter Phase-I trigger upgrade. A prototype of the custom-made dual-channel optical transmitter module, the Miniature optical Transmitter (MTx), with separate transmitter optical sub-assemblies (TOSAs) has been demonstrated at data rates up to 8 Gbps per channel. A Vertical-Cavity Surface-Emitting Laser (VCSEL) driver ASIC has been developed and is used in the current MTx prototypes. A serializer ASIC prototype, operating at up to 8 Gbps per channel, has been designed and tested. A low-latency, low-overhead encoder ASIC prototype has been designed and tested. The latency of the whole link, including the transmitter latency and the receiver latency but not the latency of the fiber, is estimated to be less than 57.9 ns. The size of the MTx is 45 mm x 15 mm x 6 mm.

Integrated Spatial Optical System for Compact 28-Gb/s <inline-formula> <tex-math notation="TeX">\(\times \) </tex-math></inline-formula> 4-lane Transmitter Optical Subassemblies

A compact 28 Gb/s × 4-lane transmitter optical subassembly is developed for 100Gb/s Ethernet (100 GbE)/OTU4 applications with a hybrid integrated spatial multiplexer optical system. The system simply comprises three bandpass filters and a mirror, despite the narrow guardband specification. Moreover, by an intensively improved precise lens manipulation technique acting in an upward direction in addition to horizontally and downward, high-coupled power into the single-mode output fiber can be achieved, with resolving the previously reported issue that the controllable direction was limited. Finally, we show that eye diagrams with adequate mask margins (≥15%) and high extinction ratio (≥8 dB) are obtained at 28 Gb/s with a low modulating voltage (≤1.6 Vpp).

A 1.55 <inline-formula><tex-math>$\mu$</tex-math></inline-formula>m 40 Gbps EML TOSA Employing a Novel FPC Connection

We have developed a 1.55-μm 40 Gbps electro-absorption modulator laser (EML)-based transmitter optical subassembly (TOSA) using a novel flexible printed circuit (FPC). The return loss at the junctions of the printed circuit board and the FPC, and of the FPC and the ceramic feedthrough connection was held better than 20 dB at up to 40 GHz by a newly developed three-layer FPC. The TOSA was fabricated and demonstrated a mask margin of >16% and a path penalty of <0.63 dB for a 43 Gbps signal after 2.4-km SMF transmission over the entire case temperature range from −5° to 80 °C, demonstrating compliance with ITU-T G.693. These results are comparable to coaxial connector type EML modules. This TOSA is expected to be a strong candidate for 40 Gbps EML modules with excellent operating characteristics, economy, and a small footprint.

Compact packaging for multi-wavelength DML TOSA

A compact multi-wavelength hybrid-integrated directly-modulated distributed-feedback laser (DML) transmitter optical sub-assembly (TOSA) has been achieved in our laboratory. The 8-channel distributed feedback (DFB) lasers are monolithically integrated based on the reconstruction-equivalent-chirp (REC) technology. With the high-density and high-speed packaging technique, the laser array and a multi-mode interference (MMI) multiplexer are assembled in the TOSA. The channel spacing of the TOSA is 200 GHz between adjacent lasers. It meets the 8 × 12.5 Gb/s operation demand and gives rather low channel crosstalk of less than −25 dB. This compact TOSA is of effective cost and shows good stability for mass production, which is expected to improve the performance of devices in access networks, data centers and supercomputing.

Compact 100 Gb/s Ethernet Transmitter Optical Sub-Assembly Using Polarization Beam Combiner

A compact transmitter optical sub-assembly (TOSA) has been developed for a 100 Gb/s Ethernet system with a long transmission distance of 40 km over single-mode fiber. The TOSA consists of electro-absorption modulator integrated distributed feedback laser diode arrays and a polarization beam combiner for wavelength multiplexing to obtain a high optical output power and a high dynamic extinction ratio. We confirmed that the TOSA successfully achieved an error-free four-lane ×25.8 Gb/s transmission, i.e., a total bit-rate of 100 Gb/s, over 40 km.

The miniature optical transmitter and transceiver for the High-Luminosity LHC (HL-LHC) experiments

We present the design and test results of the Miniature optical Transmitter (MTx) and Transceiver (MTRx) for the high luminosity LHC (HL-LHC) experiments. MTx and MTRx are Transmitter Optical Subassembly (TOSA) and Receiver Optical Subassembly (ROSA) based. There are two major developments: the Vertical Cavity Surface Emitting Laser (VCSEL) driver ASIC LOCld and the mechanical latch that provides the connection to fibers. In this paper, we concentrate on the justification of this work, the design of the latch and the test results of these two modules with a Commercial Off-The-Shelf (COTS) VCSEL driver.

Low-Loss Cascaded Mach–Zehnder Multiplexer Integrated $25\hbox{-}{\rm Gbit}/{\rm s}\times 4\hbox{-}{\rm Lane}$ EADFB Laser Array for Future CFP4 100 GbE Transmitter

A 4 × 25-Gb/s electroabsorption modulator integrated with a distributed feedback (DFB) laser (EADFB laser) array monolithically integrated with a low-loss optical multiplexer (MUX) is developed for 100 GbE transmitters for the first time. A cascaded Mach-Zehnder (MZ) filter, which has no intrinsic loss, is used as the MUX. The design and fabrication of the MZ-MUX for 100 GbE are thoroughly described. The measured loss of fabricated MZ-MUX is 2-3 dB, which is improved by 4 dB compared with that of the conventional 1 × 4 multimode interference MUX. The MZ-MUX is monolithically integrated with a four-EADFB-laser array and the output power of the chip is increased by 3 dB compared with that of a conventional 4 × 25-Gb/s monolithically integrated chip. With the folded layout, the size of the chip is similar to that of the conventional chip. The fabricated chip is packaged into a very compact transmitter optical subassembly (TOSA). The system requirements are satisfied with semi-cooled operation, and very clear eye openings are obtained after 10-km single-mode-fiber transmission. The adjustment of filter spectra by current injection is also shown, and fine tuning is possible with very low injection current.

A cost-effective 25-Gb/s EML TOSA using all-in-one FPCB wiring and metal optical bench

We present a cost-effective 25-Gb/s electro-absorption modulator integrated laser (EML) transmitter optical sub-assembly (TOSA) using all-in-one flexible printed circuit board (FPCB) wiring and a metal optical bench (MOB). For a low cost and high bandwidth TOSA, internal and external wirings and feed-through of the TOSA to transmit radio-frequency (RF) signal are configured all-in-one using the FPCB. The FPCB is extended from an exterior of the TOSA package up to an EML chip inside the package through the slit formed on a rear sidewall of the package and die-bonded on the MOB. The EML TOSA shows a modulated output power of more than 3.5 dBm and a clear eye pattern with a dynamic extinction ratio of ~8.4 dB at a data rate of 25.78 Gb/s.

Lens Alignment Technique Using High-Power Laser for Hybrid Integrated Multi-Channel Transmitter Optical Sub-Assemblies

We propose a precise submicrometer alignment technique for lenses employing high-power laser irradiation. We investigate the mechanism in detail, and show that manipulation of the lenses is achieved in all directions, for the tightest positional tolerance. In particular, our proposed technique enables lens alignment by irradiating only the top of the lens holder making it suitable for high-density integrated multi-channel systems. With this technique, we have successfully developed the first lens-coupled hybrid integrated optical system for a 100 Gbit/s Ethernet transmitter optical sub-assembly.

Ultra-Compact 100 GbE Transmitter Optical Sub-Assembly for 40-km SMF Transmission

The first ultra-compact transmitter optical sub-assembly (TOSA) has been developed for the metro-area 100 Gbit/s Ethernet (100 GbE) system. Four DFB lasers integrated with electro-absorption modulators (EADFB lasers) operated at 25.8 Gbit/s and an optical multiplexer are monolithically integrated on one chip. The chip was assembled in the compact TOSA using a three-dimensional (3D) RF circuit board supported by a spacer. The new structure provides compact and high-density interconnection with low crosstalk between RF signal lines. The TOSA is very small at just 8.0 mm × 35 mm × 6.5 mm including the receptacle and the flexible printed circuit (FPC) and could be installed in next-generation small form 100 GbE transceivers. In addition, an error-free transmission is demonstrated through 40 km of single-mode fiber at 100 Gbit/s with a modulation voltage of 2 V.

Ultracompact, 160-Gbit/s transmitter optical subassembly based on 40-Gbit/s × 4 monolithically integrated light source

The first ultracompact transmitter optical subassembly for long-distance, beyond-100-Gbit/s data communication systems based on a monolithically integrated light source is developed. The light source consists of four InGaAlAs-based electroabsorption modulator integrated DFB lasers (EADFB lasers) and their optical multiplexer and these components are monolithically integrated on one chip, resulting in very small chip size of 2.4 × 3.3 mm2. This small chip makes it possible to reduce the size of the transmitter module. Very small transmitter optical subassemblies (TOSAs), using the chip and employing three-dimensional interconnection board, is fabricated, whose volume is only 1.82 cc. By using the TOSA, 40-Gbit/s × 4 operation with the clear eye openings up to 10-km single mode fibre transmission is demonstrated. Electrical crosstalk under the multi-lane operation is also evaluated, and the error-free transmission is achieved with the power penalty to the discrete operation of 1 dB.

A 25 Gbit/s Transmitter Optical Sub-Assembly Package Employing Cost-Effective TO-CAN Materials and Processes

A cost-effective 25 Gbit/s directly modulated transmitter optical sub-assembly (TOSA) employing transistor outline (TO)-CAN materials and processes is demonstrated. A high speed distributed feedback laser diode (DFB LD) chip used in the TOSA is characterized by a directly high frequency probing measurement and an equivalent circuit model according to the measurement result. Using a TOSA package with TO-CAN structure and applying the deduced equivalent circuit model of the DFB LD chip in the simulation, a modified TOSA is proposed. The parasitic effect of bonding-wire and the gap induced in die bonding process is studied comprehensively to achieve an optimum configuration. Based on the simulated result, the proposed TOSA is fabricated through a conventional TO-CAN and TOSA fabrication process. The measured results show that the TOSA exhibits a 3-dB bandwidth of 18.7 GHz and a clearly opening eye diagram of 25 Gbit/s. This developed TOSA is potential for use in the next generation fiber network of 25 Gbit/s or 100 Gbit/s due to advantages of cost-effective design and mass production capability.

10-Gbps electroabsorptive modulated laser bidirectional optical subassembly using novel two-window flat package for passive optical network

A novel 10-Gbps bidirectional optical subassembly (BOSA) comprised of a 1577 nm electroabsorptive modulated laser (EML) transmitter optical subassembly (TOSA) and 1270 nm avalanche photodiode (APD) receiver optical subassembly (ROSA) was developed. Here, a 10-Gbps microdevice compatible two-window flat package was proposed to simplify the EML BOSA structure, considering both the mechanical reliability and cooling performance. As a result, an optical output power of 8 dBm was obtained due to a high optical coupling efficiency of 60%, an extinction ratio of 7 dB, and a dispersion penalty at 20 km transmission of less than 1.5 dB for the EML TOSA. The APD ROSA sensitivity was -21.5 dBm at a bit error rate (BER) of 10−12 and -27 dBm at a BER of 10−3 without forward error correction. In addition, the sensitivity penalty of the APD ROSA due to signal crosstalk was less than 1.2 dB.

Long-Reach 100Gbit Ethernet Light Source Based on 4*25-Gbit/s 1.3-.MU.m InGaAlAs EADFB Lasers

High-performance 1.3-µm electroabsorption modulators integrated with DFB lasers are developed for long-reach 100Gbit Ethernet. The dynamic extinction ratio of over 8-dB with the voltage swing of 2V are achieved for the four LAN-WDM lanes (14nm wavelength range) used in 100Gbit Ethernet with the same modulator structure. The fabricated devices are packaged in butterfly modules and four-lane 40-km single mode fiber transmission at 25-Gbit/s operation is demonstrated. Further, a can-type transmitter optical subassembly is fabricated to reduce the cost and size of transmitter modules. The use of a low-dielectric-constant liquid crystal polymer transmission line makes the 3-dB bandwidth larger and enables 25-Gbit/s operation with CAN-TOSA module.

Design and fabrication of a transmitter optical subassembly (TOSA) in 10-gb/s small-form-factor pluggable (XFP) transceiver

A smart and compact packaging transmitter optical subassembly (TOSA) in a 10-Gb/s small-form-factor pluggable (XFP) transceiver module has been developed with an eye towards electrical and thermal performances. In the TOSA, a bias-tee circuit and a matching resistor are monolithically integrated on an AlN submount with high thermal conductivity, and a newly proposed coplanar waveguide is drawn in a transistor outline (TO)-stem. In order to improve the electrical performance of the TOSA, the equivalent circuit model of all optoelectronic components in the TOSA is introduced and utilized. The fabricated TOSA shows the -3-dB bandwidth as high as 11 GHz and 0.36-dB penalty after a 75-km transmission at an elevated temperature of 85degC

10 Gb/s XFP Transceiver용 Transmitter Optical Sub-assembly(TOSA)의 RF 설계/제작 및 주파수 특성 해석

XFP(10 Gb/s Small Form Factor Pluggable) 트랜시버 모듈에 사용되는 광송신 서브어셈블리(TOSA: Transmitter Optical Sub-assembly)를 열적, 전기적 측면에서 설계, 제작 및 평가하였다. 저가격이며 소형인 TOSA를 제작하기 위해서 바이어스 티 및 정합저항등을 AlN서브마운트 위에 집적하였다. 10 Gb/s의 초고속 전기 신호의 입력을 위해 CPW형 마이크로파 전송로를 스템 구조체내에 도입하였다. 소자의 전기적 특성 분석을 위해 서브마운트내에 실장되는 각종 전기광학 부품들과 스템 구조체들을 고속회로 모델링 하였다. 제작한 TOSA의 특성평가를 통해, 85<TEX>$^{\circ}C$</TEX>에서 11 GHz 이상의 -3 dB 대역폭을 얻을 수 있었다. As a transmitter sub-assembly in the XFP(10 Gb/s Small Form Factor Pluggable) transceiver module, a transmitter optical sub-assembly(TOSA) is designed, fabricated and characterized in view of electrical and thermal performances. For a low-cost and compact packaging TOSA, the bias-tee and the matching resistor are monolithically integrated on the AlN sub-mount and a newly designed coplanar waveguide is drawn in the TO-stem. All optoelectronic components packaged in the TOSA are modeled by the equivalent circuit, which helps to improve and characterize the TOSA performance. The fabricated TOSA shows the -3㏈ bandwidth as high as 11 GHz at an elevated temperature of 85<TEX>$^{\circ}C$</TEX>.

Modeling and simulation of next-generation multimode fiber links

This paper describes an advanced multimode-fiber-link model that was used to aid the development of Telecommunication Industry Association standard specifications for a next-generation 50-μm-core laser-optimized multimode fiber. The multimode-link model takes into account the interactions of the laser, the transmitter optical subassembly, and the fiber, as well as effects of connections and the receiver preamplifier. We present models for each of these components. Based on these models, we also develop an efficient and simple formalism for the calculation of the fiber transfer function and the signal at the link output in any link configuration. We demonstrate how the model may be used to develop specifications on transmitters and fibers that guarantee any desired level of performance.

Demonstration of a small-form-factor WWDM transceiver module for 10-Gb/s local area networks

We demonstrate for the first time all key components for a small-form-factor (SFF) wide-wavelength-division-multiplexed (WWDM) transceiver module with four channels operating at a data rate of 3.125 GBd/channel giving an aggregate rate of 12.5 GBd. The key components that enable a SFF package include a compact injection-molded plastic demultiplexer and a compact transmitter optical subassembly. We report link results showing successful operation of these key components with transmission over 300 m of 62.5-μm core multimode fiber (MMF) and 10.5 km of single-mode fiber (SMF). These technologies enable highly-integrated WWDM 10-Gb Ethernet transceiver modules that support both MMF and SMF.