Transmitter Optical Subassembly Research Articles

Low-cost hybrid integrated 4 × 2578 Gb/s CWDM TOSA for 10 km transmission using DFB-LDs and an arrayed waveguide grating multiplexer

We have developed a cost-effective and highly compact 100-Gb/s coarse wavelength division multiplexing (CWDM) transmitter optical subassembly (TOSA) using lens-free hybrid integration. To achieve large alignment tolerances, distributed feedback laser diodes (DFB-LDs) are butt-coupled to a four-channel silica-based planar lightwave circuit (PLC) arrayed waveguide grating, with the silicon sub-mounts and PLC adhesively bonded. Then, a flexible printed circuit is employed to connect the internal DFB-LDs and the exterior of the TOSA package for radiofrequency signal transmission, eliminating the expensive ceramic feed-through. The packaged CWDM TOSA, which is 15.8 mm×7.0 mm×6.0 mm in size, shows a side-mode suppression ratio of >40 dB, a 3 dB bandwidth of >18 GHz, and error-free transmission with an average optical output power of >0 dBm and dynamic extinction ratio of >4.0 dB at 25.78125 Gb/s over a 10 km single-mode fiber for all four lanes.

Low‐cost coaxial DFB LD transmitter optical subassembly for 25 Gb/s NRZ and 50 Gb/s PAM‐4 transmissions

Here, a directly modulated coaxial distributed feedback (DFB) laser diode (LD) transmitter optical subassembly (TOSA) module is proposed for 25 Gb/s non-return-to-zero (NRZ) and 50 Gb/s four-level pulse amplitude modulation (PAM-4) transmissions. A low-cost TO-56 header was used in the DFB LD TOSA package. The high-frequency performance of the coaxial 1310 nm DFB LD TOSA module was simulated and analysed. The simulated frequency response can correspond with the measured result, and the 3 dB bandwidth was 19 GHz. In the back-to-back and 10 km signal mode fibre transmissions, 25 Gb/s NRZ and 50 Gb/s PAM-4 eye diagrams of the DFB LD TOSA were measured. Clear 25 Gb/s NRZ and 50 Gb/s PAM-4 eye openings can be observed. For 25 Gb/s NRZ transmissions, the received sensitivity was −11.8 dBm under a bit error rate (BER) of 10 −12 . For 50 Gb/s PAM-4 transmissions, the BER was estimated to be below the forward error correction threshold. The low-cost coaxial DFB LD TOSA is suitable in 100, 200, and 400 Gb/s transmissions.

Integrated four-channel directly modulated O-band optical transceiver for radio over fiber application.

We have fabricated a compact and integrated 4-channel analog optical transceiver for radio over fiber application. In the fabricated module, the transmitter optical sub-assembly is composed of four directly modulated DFB laser chips integrated with an optical multiplexer based on an arrayed waveguide grating (AWG) using silica-based planar lightwave circuit (PLC) technology. The receiver optical sub-assembly consists of a PIN photodiode array integrated with an AWG-PLC-type optical de-multiplexer. For all the lanes, the 3 dB bandwidth exceeds 19.1 GHz and the measured spurious-free dynamic range (SFDR) is up to 90.5 dB⋅Hz2/3 when the input RF frequency is from 2 GHz to 14 GHz. Meanwhile, the electrical inter-channel crosstalk of the transceiver is less than -20 dB when the carry frequency is below 18.5 GHz. This module shows a great transmission performance in radio over fiber system. Under simultaneous 4-channel different 600 Mb/s 5-band 64QAM-OFDM RF signal operation, the measured error vector magnitude (EVM) performance below 8% is achieved after 15.5 km single-mode fiber propagation for all lanes. This scheme has potential applications in guiding high-dense, cost-effective and high-linearity analog optical transceiver design to realize high-capacity radio over fiber transmission systems.

200 Gb/s FSO WDM Communication System Empowered by Multiwavelength Directly Modulated TOSA for 5G Wireless Networks

In this paper, a 200-Gb/s free-space optical (FSO) wavelength division multiplexing (WDM) transmission architecture based on multiwavelength directly modulated transmitter optical sub-assemblies for 5G wireless networks has been proposed and demonstrated experimentally. Pulse amplitude modulation-4 (PAM-4) modulation format is adopted in our scheme to further improve system capacity. In order to demonstrate the feasibility of our scheme, the outdoor experiments with 25 Gb/s PAM-4 are tested in free space. With 8 × 25 Gb/s ~50-m outdoor transmission between the two buildings, the eye diagrams and bit error rates (BERs) are tested for one-hop system and forwarding system, respectively. For one-hop system, clear eye diagrams and stable BER performance are demonstrated in all the wavelengths. For the forwarding system, the values of BER with eight channels are measured lasting for 30 min that range from 1E-2 to 1E-3. The experimental results show that the scheme is feasible in FSO transmission system for 5G wireless networks. The advantages of integration, channelization, miniaturization, and low power consumption of the FSO WDM scheme present a promising result on constructing the future fronthaul/backhaul link for wireless cellular networks and optical access network extension.

First demonstration of a 400 Gb/s 4λ CWDM TOSA for datacenter optical interconnects.

We present the first demonstration of a 4λ transmitter optical sub-assembly (TOSA) on the coarse wavelength division multiplexing (CWDM) grid, i.e., 20 nm spacing, targeting 400G-FR4 requirements over 2 km. The TOSA is based on uncooled InP external modulated laser (EML) technology and it utilizes four EMLs followed by a CWDM multiplexer. We characterize the performance of the TOSA versus received optical modulation amplitude (OMA), number of equalizer taps, reach, modulation format, TOSA case temperature, and bit rate. Four 53 Gbaud 4-level pulse amplitude modulation (PAM4) RF signals are used to drive the TOSA achieving a net rate of 400 Gb/s. Results reveal that 400 Gb/s can be transmitted over 2 km of single mode fiber (SMF) at a bit error rate (BER) below the KP4- forward error correction (KP4-FEC) threshold (i.e., 2.4 × 10-4) using only a 5 tap feed forward equalizer at the receiver. To the best of our knowledge, this is the first demonstration of 400 Gb/s using a 4λ CWDM TOSA over 2 km of SMF. Moreover, we achieve 400 Gb/s and 600 Gb/s over 20 km and 10 km below KP4-FEC and the 7% hard-decision FEC (HD-FEC) (i.e., 3.8 × 10-3) thresholds, respectively, without optical amplification. Furthermore, we show the performance of the TOSA against temperature, where it shows no significant change in the BER performance from 20 °C to 60 °C. Finally, we compare the performance of PAM2, PAM4, and PAM8 modulation formats where we show the possibility of achieving 400 Gb/s aggregate bit rate using 42 Gbaud PAM8 modulation format at the expense of utilizing a stronger FEC.

Hybrid silica coarse wavelength-division multiplexer transmitter optical subassembly

Based on silica arrayed waveguide grating technology, a hybrid integrated transmitter optical subassembly was developed. Four direct-modulating distributed feedback lasers and four focusing microlenses were integrated to a coarse wavelength-division multiplexer (CWDM) on a CuW substrate. The four-channel silica-on-silicon CWDM was fabricated with 1.5% refractive index difference and 20-nm wavelength spacing. The experimental results showed that the output optical power was >3 mW with 45 mA of injection current, the slope efficiency was >0.0833 W/A, and the 3-dB bandwidth was broader than 18.15 GHz. The 1-dB compress points were higher than 18 and 15.8 dBm for frequency of 10 and 18 GHz, respectively.

112 Gbit/s transmitter optical subassembly based on hybrid integrated directly modulated lasers

Based on the hybrid integration technology, an ultra-compact and low cost transmitter optical subassembly module is proposed. Four directly modulated lasers are combined with a coarse wavelength division multiplexer operated at the O-band. The bandwidth for all channels is measured to be approximately 3 GHz. The 112 Gb/s transmission is experimentally demonstrated for a 10 km standard single mode fiber (SSMF), in which an optical isolator is used for avoiding the back-reflected and scattered light to improve the bit error rate (BER) performance. A low BER and clear eye opening are achieved for 10 km transmission.

Design of a Silicon Fresnel Lens for Optimized Light Coupling in a Transmitter Optical Subassembly

Design of a Silicon Fresnel Lens for Optimized Light Coupling in a Transmitter Optical Subassembly

Design and fabrication of a small‐form transmitter optical subassembly for 100 Gbps short reach optical interconnect

AbstractA high‐coupling‐efficiency and convenient‐integration transmitter optical subassembly for 25 Gbps small‐form transceiver is developed in this paper. In the structure, the VCSEL is vertically mounted on the silicon substrate by the flip‐chip method to enable direct and passive alignment with the fibers plugging in the fiber guide holes on the silicon substrate. By the optical simulation, the maximum coupling efficiency of VCSEL is −0.38 dB. The vertical electrical pads of the VCSEL are connected to the horizontal wire‐bonding pads on silicon substrate by the 90°‐bend GS micro strip lines. Thus, the interconnection between the transmitter optical subassembly and the electrical PCB board is conveniently realized by the low‐cost wire‐bonding method. The electrical performance of the 90°‐bend GS micro strip lines on the optical subassembly is also evaluated by the 3D electromagnetic simulation. In order to verify the transmission performance of the transmitter optical subassembly, it is integrated with an electrical board using bonding wires, and then the optical performance of the transmitter is measured. By the measurement, the optical subassembly can operate up to 25 Gbps per channel.

SWDM PAM4 Transmission From 850 to 1066 nm Over NG-WBMMF Using 100G PAM4 IC Chipset With Real-Time DSP

The 53.125 Gbps transmission is experimentally investigated over a next-generation wideband multimode optical fiber (NG-WBMMF) using transmitter optical sub-assemblies (TOSAs) and wideband receiver optical sub-assemblies (ROSAs) developed for 25 Gbps short wavelength division multiplexing (SWDM) operation. A commercial 100 Gbps four-level pulse amplitude modulation integrated circuit (PAM4 IC) evaluation kit with real-time digital signal processing (DSP) is used. Dual wavelength transmission (2 λ × 53.125 Gbps) tests over 300 m of NG-WBMMF are carried out for the wavelength pairs 850, 880 nm and 910, 940 nm with a 4 × 1 optical MUX/DeMUX in the link. Measured pre-forward error correction (FEC) bit error ratio (BER) below the KP4 FEC threshold of 2.4 × 10–4 indicates the feasibility of 100/200 Gbps transmission over NG-WBMMF using a PAM4 chipset with real-time DSP. Single wavelength transmission (1 λ × 53.125 Gbps) using long wavelength TOSAs at 976 and 1066 nm is also studied. Pre-FEC BER below 2.4 × 10–4 is achieved over 300 m at 976 nm and 200 m at 1066 nm. Single wavelength tests from 850 to 940 nm had the same results as the 976 nm wavelength. Thus, this is the first experiment which shows the potential of 400 Gbps transmission with eight SWDM wavelength windows over a single NG-WBMMF using SWDM TOSAs, ROSAs, and commercial 100 Gbps PAM4 chipset.

30-km Error-Free Transmission of Directly Modulated DFB Laser Array Transmitter Optical Sub-Assembly for 100-Gb Application

We fabricated the first compact 100-gigabit Ethernet (100GbE) transmitter optical sub-assembly (TOSA) using a directly modulated DFB laser (DML) array monolithically integrated with an optical multiplexer. Specially designed InGaAlAs/InGaAlAs multiple quantum wells make it possible to obtain a large gain in the 1295–1310-nm wavelength range and to operate at a high temperature of 55 °C. The four-channel DML array chip is only $2.0 \,\text{mm} \times 2.4 \,\text{mm}$ in size, and the fabricated TOSA is only $7.2 \,\text{mm} (W) \times 14.3 \,\text{mm} (L) \times 6.5 \,\text{mm} (H)$ , which fits a CFP2 or smaller 100-GbE transceiver. For all the lanes, the 3-dB bandwidths of the TOSA exceeded 17 GHz, and it could operate at 25.8 Gb/s. With 25.8-Gb/s × four-channel simultaneous operation, error-free transmissions over a 30-km single-mode fiber were demonstrated for all the lanes.

Bidirectional optical subassembly-shaped 20 - Gbit / s compact single-mode four-channel wavelength-division multiplexing optical modules for optical multimedia interfaces

Low-cost single-mode four-channel optical transmitter and receiver modules using the wavelength-division multiplexing (WDM) method have been developed for long-reach fiber optic applications. The single-mode four-channel WDM optical transmitter and receiver modules consist of two dual-wavelength optical transmitter and receiver submodules, respectively. The integration of two channels in a glass-sealed transistor outline-can package is an effective way to reduce cost and size and to extend the number of channels. The clear eye diagrams with more than about 6 dB of the extinction ratio and the minimum receiver sensitivity of lower than −16 dBm at a bit error rate of 10−12 have been obtained for the transmitter and receiver modules, respectively, at 5 Gbps/channel. The 4K ultrahigh definition contents have been transmitted over a 1-km-long single-mode fiber using a pair of proposed four-channel transmitter optical subassembly and receiver optical subassembly.

Low-crosstalk operation of directly modulated DFB laser array TOSA for 112-Gbit/s application.

A directly modulated DFB laser (DML) array transmitter optical sub-assembly (TOSA) operating at 112 Gbit/s was fabricated for the first time. The DML array chip, which was integrated with a GND pad, and the DML array sub-assembly were designed to suppress the adjacent electrical crosstalk of the DML array TOSA. The 3-dB bandwidths of the fabricated TOSA exceeded 18 GHz. The electrical crosstalk of the TOSA was suppressed to less than -20 dB below 18GHz. Under simultaneous 4-channel 28-Gbit/s (112 Gbit/s) operation, the OTU4 mask margins were degraded by a maximum of only 6% compared with those under discrete operation. Error-free transmissions over a 10-km single-mode fiber were demonstrated for all the lanes under 112-Gbit/s operation.

Aging and environmental tolerance of an optical transmitter for the ATLAS Phase-I upgrade at the LHC

The dual channel Miniature optical Transmitter (MTx) is developed for the ATLAS Phase-I upgrade requiring durable performance in the Large Hadron Collider environment. The data transmission has achieved 8Gbps per channel with a custom-designed LOCld laser driver and 850nm VCSELs packaged in transmitter optical sub-assemblies (TOSAs). The performance of the MTx opto-electronics is evaluated. Accelerated aging tests of the VCSELs were conducted in a chamber at 85°C, 85% relative humidity, with TOSA and bare-die samples prepared in non-hermetic condition. Radiation tolerance of the VCSELs was investigated with 30MeV and 70MeV protons. The radiation induced effects in data transmission were investigated for light-power degradation and parameters of eye-diagrams.

Extended-Temperature Operation (−40 °C to +95 °C) of an EML TOSA Employing an Athermal Optical System

An electroabsorption-modulated laser (EML) transmitter optical sub-assembly (TOSA) employing an athermal optical system has been demonstrated for extended-temperature operation from −40 °C to 95 °C. The output power variation of the TOSA was held to <0.3 dB over this wide temperature range because of optical compensation using the thermo-optical properties of the plastic lens. A 0.8-dB improvement over the variation without this compensation was confirmed. Since the TOSA has sufficient electrical bandwidth for 20-Gb/s operation, clear eye openings with an extinction ratio of over 9.7 dB were obtained over the wide temperature range. The heat sink, the size of which was optimized for operation of the EML at 55 °C, enabled the TOSA to operate over the wide temperature range without thermal runaway. As a result, power consumption of <0.42 W was achieved over the temperature range.

Compact Hybrid-Integrated 100-Gb/s TOSA Using EADFB Laser Array and AWG Multiplexer

We have developed a compact hybrid-integrated four-lane $\times 25.8$ Gb/s transmitter optical sub-assembly (TOSA) for a 100 Gb/s transceiver for 40-km transmission. The TOSA has a simple configuration in which a four-channel electroabsorption modulator integrated distributed feedback (EADFB) laser array is directly attached to the input waveguide end-faces of a silica-based arrayed waveguide grating (AWG) multiplexer. We integrated a lateral tapered spot-size converter for the EADFB laser to achieve a high optical butt coupling efficiency between the EADFB lasers array and the AWG multiplexer. We confirmed that the TOSA, which is $19.9~\text {mm} \,\times \, 6~\text {mm} \,\times \, 5.8$ mm, achieved error-free operation for a 40-km transmission with a high average optical output power of over 0.3 dBm at an operating temperature of 55 °C.

Compact Hybrid Integrated 100-Gb/s Transmitter Optical Sub-Assembly Using Optical Butt-Coupling Between EADFB Lasers and Silica-Based AWG Multiplexer

A compact hybrid-integrated 100 Gb/s (4 lane × 25.78125 Gb/s) transmitter optical sub-assembly (TOSA) has been developed for a 100 Gb/s transceiver for 40-km transmission over a single-mode fiber. The TOSA has a simple configuration in which four electro-absorption modulator-integrated distributed feedback (EADFB) lasers are directly attached to the input waveguide end-face of a silica-based arrayed waveguide grating (AWG) multiplexer without bulk lenses. To achieve a high optical butt coupling efficiency between the EADFB lasers and the AWG multiplexer, we integrated a laterally tapered spot-size converter (SSC) for the EADFB laser and employed a waveguide with a high refractive index difference of 2.0% for the AWG multiplexer. By optimizing the laterally tapered SSC structure, we achieved a butt-coupling loss of less than 3 dB, which is an improvement of around 2 dB compared with a laser without an SSC structure. We also developed an ultracompact AWG multiplexer, which was 6.7 mm × 3.5 mm in size with an insertion loss of less than 1.9 dB. We achieved this by using a Mach–Zehnder interferometer-synchronized configuration to obtain a low loss and wide flat-top transmission filter spectra. The TOSA body size was 19.9 mm (L) × 6.0 mm (W) × 5.8 mm (H). Error-free operation was demonstrated for a 40-km transmission when all the lanes were driven simultaneously with a low EA modulator driving voltage of 1.5 V at an operating temperature of 55 °C.

Low Switching Voltage Mach–Zehnder Modulator Monolithically Integrated With DFB Laser for Data Transmission up to 107.4 Gb/s

We present a transmitter optical subassembly consisting of an InP-based travelling wave electrode Mach–Zehnder modulator monolithically integrated with a distributed feedback laser. At 56-Gb/s non-return-to-zero ON/OFF keying (NRZ-OOK), we achieve 3.5-km transmission before breaking the hard decision forward error correction threshold (3.8 ×10−3). 9-km transmission is achieved at 71.6-Gb/s 4-pulse–amplitude modulation (PAM4) and 5 km at 107.4 Gb/s PAM8. The modulation voltage is between 1.5 and 2 V, leading to overall power consumption of 171 mW for the NRZ-OOK case and 206 mW at PAM4 and PAM8.

Transmitter Optical Subassembly Using a Polarization Beam Combiner for 100 Gbit/s Ethernet over 40-km Transmission

A transmitter optical subassembly (TOSA) has been developed for a 100-Gbit/s Ethernet system for a long optical transmission distance over a 40-km single-mode fiber (SMF). To obtain a high optical output power and a high dynamic extinction ratio, the TOSA consists of two two-channel distributed feedback laser diode array chips integrated with electro-absorption modulators (EADFB laser array chips) with a 2 × 1 multimode interference (MMI) optical coupler and a polarization beam combiner for wavelength multiplexing. The TOSA is 8.7 mm × 28.7 mm × 6.5 mm including an LC-type receptacle. The TOSA has a twin collimator path for two EADFB laser array chips. The wavelength multiplexer consists of a mirror, a half-wavelength plate, and a polarization beam combiner. The TOSA could improve the optical output power by around 2 dB compared with a TOSA with a four-channel EADFB laser array chip and a 4 × 1 MMI optical coupler. An optical modulation amplitude of over 0.5 dBm and a mask margin exceeding 21% were obtained for each lane when all lanes were operated simultaneously with an EA modulator driving voltage of 1.5 V at a bit rate of 25.78125 Gbit/s, which fully satisfies the 100GBASE-ER4 specifications. We demonstrated error-free operation for an SMF transmission of over 40 km. Moreover, we confirmed that the TOSA was capable of error-free SMF transmission over 60 km with a power penalty of less than 1.4 dB.

Compact High-Responsivity Receiver Optical Subassembly With a Multimode-Output-Arrayed Waveguide Grating for 100-Gb/s Ethernet

We developed a compact receiver optical subassembly (ROSA) for 100-Gigabit Ethernet (100 GbE) using multimode-output-arrayed waveguide grating (MM-AWG) and arrayed photodiodes (PDs). The four-channel silica-based MM-AWG has low insertion loss of less than 1 dB. The back-side-illumined PD with maximized-induced current structure provides high responsivity of 0.95 A/W. To avoid the distortion of the responsivity spectrum due to poor coupling between the multimode beam and PD, we employ a racetrack shape for the active region of the PD. The optical coupling between the MM-AWG and lens-coupled PD is optimized in terms of the flattening ratio of the racetrack shape. The fabricated ROSA has high responsivity of over 0.7 A/W with a flat-top spectrum and obtains high environmental stability thank to its large assembly tolerance of over ± 4 μm. For 4 × 25−Gb/s signals after 10-km transmission, the minimum receiver sensitivity of the ROSA has a margin of 4.8 dB for the Ethernet standard. The transmission performance with a 100-GbE transmitter optical subassembly was also confirmed.