Transmitter Optical Subassembly Research Articles

A Widely and Continuously Tunable Single-Mode Transmitter Based on a Hybrid Microcavity Laser

A method for achieving the single-mode and efficient unidirectional emission of a whispering gallery mode (WGM) semiconductor laser is presented herein. Hybrid square-rectangular lasers (HSRLs) and hybrid square/rhombus-rectangular lasers (HSRRLs) consisting of a Fabry–Pérot (FP) cavity and a square or rhombus cavity microcavity are described. In addition, a transmitter optical subassembly (TOSA) based on an HSRRL chip was fabricated, which has a wide and continuous wavelength tuning range. Wavelength channels from 1555.75 nm to 1568.15 nm with a spacing of 50 GHz were demonstrated with a good side mode suppression ratio (SMSR) and good output power. These devices have the potential to meet the typical requirements of optical communication networks.

Nano-ITLA Based on Thermo-Optically Tuned Multi-Channel Interference Widely Tunable Laser

A tunable light source with narrow linewidth, small size and low power consumption is necessary for high-speed digital coherent communication system. We have developed a monolithically integrated narrow linewidth widely tunable laser—multi-channel interference (MCI) laser, which realizes a quasi-continuous tuning range covering the C++ band. By packaging the laser chip, wavelength locker and thermoelectric cooler (TEC) into a transmitter optical subassembly (TOSA) box and designing a compact print circuit board (PCB), a nano-integrable tunable laser assembly (Nano-ITLA) based on the thermo-optically tuned MCI laser is demonstrated for the first time. The Nano-ITLA is 25.0 mm (L) × 15.6 mm (W) × 6.5 mm (H), and realizes 120 International Telecommunication Union (ITU)-grid switching over 48 nm and less than 3 W total power consumption. The side-mode suppression ratios (SMSRs) are higher than 46 dB, the fiber coupled output powers are greater than 16 dBm, and the Lorentzian linewidths are less than 150 kHz. High precision wavelength locking and temperature control system make the output frequency deviation of all channels from the ITU-grid less than ± 0.5 GHz and the wavelength drift less than ± 1 pm. The output power can be accurately controlled and stabilized at ± 0.1 dB through a closed-loop feedback. The no-light shutdown function realizes an extinction ratio higher than 40 dB during wavelength switching. The Nano-ITLA demonstrates excellent application potential in the coherent optical communications.

Novel low-cost high-speed optic–electric laser diode pigtail module packaging technology

• At present, the research and development of high-speed laser modules for communication are designed with ceramic components globally. • In module packaging without the ceramic part, the misalignment caused by the deformation results in coupling efficiency loss. • A new type of high-speed laser diode pigtail module is designed to change the structure of a laser module and remove ceramic and process parts. • A laser diode pigtail module package achieves the best coupling efficiency. A high-speed laser diode pigtail for wide-band fiber-optic communications is a key component in optical fiber user loop systems, optical fiber data communication systems, and cable television systems. With the advent of a new type of optic–electric high-speed laser, wide-band communication has emerged. These three systems constitute future mainstreams of optical fiber communications. However, high-speed laser diode pigtails used in module components and process assembly account for extremely high production costs. The proposed pigtail module eliminates ceramic parts and facilitates mass production of the components. An optic fiber (including a jacket) was placed into a ferrule sleeve. The optic fiber did not undergo laser damage, and its stability in the reliability test was ensured by the plastic jacket. The optic fiber terminal surfaces grind the 7° angle to enhance the surface quality of the connector, thereby avoiding reflection and incurring a power loss of 4%. Moreover, achieving alignment in a conventional laser module package without a ceramic part and fiber ferrule is a considerable challenge, and apparently, there are still some issues that need to be resolved. In conventional optical fiber module package, laser welding technique provides a superior joint strength. However, in module packaging without the ceramic part, the misalignment caused by the deformation results in coupling efficiency loss. Therefore, a novel design of laser diode pigtail module packaging is necessary. A transmitter optical subassembly device, receiver optical subassembly device, and transceiver pigtail module can be manufactured in a unified process package. By applying the low-cost packaging technique, the cost and fabrication time of the module packaging were reduced, and the fabrication yield was increased.

A 20 Gbps PAM4 data transmitter ASIC for particle physics experiments

We present the design and test results of a novel data transmitter ASIC operating up to 20.48 Gbps with 4-level Pulse-Amplitude-Modulation (PAM4) for particle physics experiments. This ASIC, named GBS20, is fabricated in a 65 nm CMOS technology. Two serializers share a 5.12 GHz Phase Locked Loop (PLL) clock. The outputs from the serializers are combined into a PAM4 signal that directly drives a Vertical-Cavity-Surface-Emitting-Laser (VCSEL). The input data channels, each at 1.28 Gbps, are scrambled with an internal 27-1 Pseudo-Random Binary Sequence (PRBS), which also serves as a frame aligner. GBS20 is tested to work at 10.24 and 20.48 Gbps with a VCSEL-based Transmitter-Optical-Subassembly (TOSA). The power consumption of GBS20 is below 238 mW and reduced to 164 mW in the low-power mode.

5G-Compatible IF-Over-Fiber Transmission Using a Low-Cost SFP-Class Transceiver

With the rise of 5G and beyond, the ever-increasing data-rates demanded by mobile access are severely challenging the capacity of optical fronthaul networks. Despite its high reliability and ease of deployment, legacy digital radio-over-fiber (RoF) technologies face an upcoming bandwidth bottleneck in the short term. This has motivated a renewed interest in the development of analog RoF alternatives, owing to their high spectral efficiency. However, unlike its digital counterpart, analog RoF transmission requires a highly linear transceiver to guarantee signal fidelity. Typical solutions exploited in recent research works tend to adopt the use of bulky benchtop components, such as directly modulated lasers (DML) and photodiodes. Although this provides a convenient and quick path for proof-of-concept demonstrations, there is still a considerable gap between lab developments and commercial deployment. Most importantly, a key question arises: can analog-RoF transceivers meet the 5G requirements while being competitive in terms of cost and footprint? Following this challenge, in this work we exploit the use of a low-cost commercial off-the-shelf (COTS) small form-factor pluggable (SFP) transceiver, originally designed for digital transmission at 1 Gbps, which is properly adapted towards analog RoF transmission. Bypassing the digital electronics circuitry of the SFP, while keeping the original transmitter optical sub-assembly (TOSA) and receiver optical sub-assembly (ROSA), we demonstrate that high-performance 5G-compatible transmission can be performed by reusing the key built-in components of current low-cost SFP-class transceivers. Particularly, we demonstrate error vector magnitude (EVM) performances compatible with 5G 64QAM transmission both at 100MHz and 400MHz. Furthermore, employing a memory polynomial model for digital pre-distortion of the transmitted signal, we achieve 256QAM-compatible performance at 100MHz bandwidth, after 20 km fronthaul transmission.

LDLA14: a 14 Gbps optical transceiver ASIC in 55 nm for NICA multi purpose detector project

This paper presents the design and test results of a 14 Gbps optical transceiver ASIC (LDLA14) fabricated in a 55 nm CMOS technology for NICA Multi Purpose Detector (MPD) project. The LDLA14 is a single-channel bidirectional (1Tx + 1Rx) optical transceiver ASIC, including a Laser Driver (LD) module and a Limiting Amplifier (LA) module. It would drive the Vertical Cavity Surface Emitting Laser (VCSEL) of Transmitter Optical Sub-Assembly (TOSA) and receive signals from Photo Diode (PD) of Receiver Optical Sub-Assembly (ROSA), respectively. In the LDLA14, a novel structure of capacitive coupling pre-emphasis is proposed in the output driver of LD to obtain peaking effect without sacrifice the modulation current swing. A shared inductor technology and a Continuous Time Linear Equalizer (CTLE) pre-emphasis structure are added in the output buffer of LA to improve the quality of the output eye diagram. The dimension of LDLA14 is 1.5 mm × 1.3 mm, and the power consumption is 178 mW. The Peak-to-Peak Jitter (PPJ) and Root-Mean-Square Jitter (RMSJ) of the 14 Gbps optical eye diagram of LD in the Tx direction are 22.5 ps and 3.5 ps, respectively. The PPJ and RMSJ of the 14 Gbps electrical eye diagram of LA in the Rx direction are 23.1 ps and 4.7 ps, respectively. The BER tests have been conducted in Tx, Rx directions and the Tx-Rx loop condition, and the BER less than 10−12 is achieved in all tests.

Alignment tolerant analysis of a compact 4 × 25 Gbps TOSA with a thin-film filter multiplexer

A 100 Gbps transmitter optical sub-assembly (TOSA) based on a thin-film filter (TFF) multiplexer (MUX) demonstrated high alignment tolerance in a small volume. The model was based on the transfer-matrix method to investigate the effect of collimation and focus lens structures on coupling efficiency. The tolerances of the focus lens, MUX, and collimation lens were analyzed by simulation and experiment, obtaining the main values in 1 dB coupling loss of ±25, ±450, and ±3.3 um, respectively. Test results indicate that the transmission in a single mode fiber over 10 km is achieved with the 100 Gbps TOSA extinction ratio over 40 dB.

A 10-Gb/s Driver/Receiver ASIC and Optical Modules for Particle Physics Experiments

We present the design and test results of a Drivers and Limiting AmplifierS ASIC operating at 10 Gb/s (DLAS10) and three miniature optical transmitter/ receiver/transceiver modules (MTx+, MRx+, and MTRx+) based on DLAS10. DLAS10 can drive two transmitter optical subassemblies (TOSAs) of vertical cavity surface emitting lasers (VCSELs), receive the signals from two receiver optical subassemblies (ROSAs) that have no embedded limiting amplifiers (LAs), or drive a VCSEL TOSA and receive the signal from a ROSA, respectively. Each channel of DLAS10 consists of an input continuous time linear equalizer (CTLE), a four-stage LA, and an output driver. The LA amplifies the signals of variable levels to a saturation amplitude of 800 mV (peak-peak). The output driver drives VCSELs or impedance-controlled traces. DLAS10 is fabricated in a 65-nm CMOS technology. The die is 1 mm ×1 mm. DLAS10 is packaged in a 4 mm ×4 mm 24-pin quad-flat no-leads (QFNs) package. DLAS10 has been tested in MTx+, MRx+, and MTRx+ modules. Both measured optical and electrical eye diagrams pass the 10-Gb/s eye mask test. The input electrical sensitivity is 40 mVp-p, while the input optical sensitivity is -12 dBm. The total jitter of MRx+ is 29 ps (P-P) with a random jitter of 1.6 ps (rms) and a deterministic jitter of 9.9 ps. Each MTx+/MRx+ module consumes 82.6 and 174.4 mW/ch, respectively.

Multi-IF-over-fiber transmission using a commercial TOSA for analog fronthaul networks aiming beyond 5G.

An IF-over-fiber (IFoF)-based analog transport technology for mobile fronthaul applications has recently attracted significant attention. However, most previous studies have employed discrete optical components. For the analog transport technology to be a more cost-effective and power-efficient solution, it is necessary to utilize existing integrated optical transceivers. In this paper, we demonstrate IFoF transmission using a commercial off-the-shelf transmitter optical sub-assembly (TOSA). Although the TOSA was developed for a digital system employing non-return-to-zero (NRZ) signals, we show that it is also possible for the TOSA to support high-capacity analog transmission. As a demonstration, by using the TOSA, we could successfully transmit 64- and 256-ary quadrature-amplitude-modulated (64/256QAM) orthogonal-frequency-division-multiplexed (OFDM) signals with net bit rates of 54.74 and 36.49 Gbps per wavelength, respectively. Since the TOSA has four wavelength channels, the total capacities are 218.94 and 145.98 Gbps, respectively. To the best of our knowledge, these rates are the highest among all the demonstrations using analog transport technology.

Cost-minimizing distribution matching supporting net 800 Gbit/s PS-PAM transmission over 2 km using a 4-λ EML TOSA.

Probabilistic shaping (PS) allows tunable spectral efficiency that is suitable for realizing high throughput intra-data center transceivers. In this Letter, we integrate the cost-minimizing distribution matching (CMDM) in the probability amplitude shaping scheme to generate PS-PAM signals with ultra-short symbol block lengths for reduced serial processing delay. We detail the principle of CMDM and present two different methods of implementation. We demonstrate that CMDM enables the transmission of single wavelength net 200 Gbit/s PS-PAM-8 over 2 km of single-mode fiber (SMF). We show that similar performance is achievable using a constant composition distribution matcher, yet requiring 10 times longer symbol block lengths. We also report, to the best of our knowledge, the first demonstration of net 800 Gbit/s transmission over 2 km of SMF using a packaged 4-λ electro-absorption modulated laser transmitter optical sub-assembly (TOSA).

Experimental Demonstration of 600 Gb/s Net Rate PAM4 Transmissions over 2 km and 10 km with a 4-λ CWDM TOSA

We propose to introduce a controlled amount of inter-symbol interference (ISI) during pulse shaping in a high symbol rate intensity modulation direct detection (IM/DD) system to increase the alternating current (AC) power of the received electrical signal after photo-detection and transimpedance amplification. We experimentally demonstrate high-speed 4-level pulse amplitude modulation (PAM4) transmissions with a 4-λ coarse wavelength division multiplexing (CWDM) transmitter optical sub-assembly (TOSA) using the proposed scheme. The intentionally introduced ISI is mitigated using either transmitter-side Tomlinson Harashima precoding (THP) or receiver-side feed forward equalization (FFE) aided with a 2-tap post filter and maximum likelihood sequence estimation (MLSE). Both methods enable 4 × 81 Gbaud PAM4 transmission over 2 km of single mode fiber (SMF), with a bit error rate (BER) below the 7% overhead hard-decision forward error correction (HD-FEC) threshold of 3.8 × 10−3, which corresponds to a net rate of >600 Gb/s. We also explore the limit of our system at 10 km. The result shows that an aggregated net rate of 600 Gb/s excluding the HD-FEC overhead can still be achieved by loading different symbol rates onto different wavelength channels.

4 × 4 MIMO fiber-wireless transmission based on an integrated four-channel directly modulated optical transceiver

In this paper, an integrated compact four-channel directly modulated analog optical transceiver is proposed and fabricated. The 3 dB bandwidth of this optical transceiver exceeds 20 GHz, and the measured spurious-free dynamic range is up to 91.2 dB·Hz2/3. The optical coupling efficiency (CE) is improved by using a precise submicron alignment technique for lens coupling in a transmitter optical subassembly, and the highest CE is achieved when the oblique angle of the arrayed waveguide grating using a silica-based planar lightwave circuit (AWG-PLC) in receiver optical sub assembly is set to 42°. Based on the proposed optical transceiver, we have experimentally demonstrated a 6.624 Gbit/s 4×4 multi-input multioutput (MIMO) 16-quadrature amplitude modulation orthogonal frequency division multiplexing (16QAM-OFDM) radio signal over 15.5 km standard single mode fiber, together with 1.2 m wireless transmission in both an uplink and a downlink. To cope with the channel interference and noise of the fiber-wireless transmission system, a low-complexity MIMO demodulation algorithm based on lattice reduction zero-forcing (LR-ZF) is designed. In our experiment, 1.6 dB power penalty is achieved by using the proposed LR-ZF algorithm, compared to the commonly used zero-forcing algorithm. Moreover, this LR-ZF algorithm has much less complexity than the optimal maximum-likelihood sequence estimation (MLSE) at a given transmission performance. These results not only demonstrate the feasibility of the integrated optical transceiver for MIMO fiber-wireless application but also validate that the proposed LR-ZF algorithm is effective to eliminate the interference for hybrid fiber-wireless transmission.

Design of driving circuit for chaotic lasers with different thermoelectric coolers

In order to effectively regulate and control the temperature and the driving current of chaotic lasers with different thermoelectric coolers (TECs), we optimize the circuit on the basis of the previous circuit design. The new circuit achieves effective control of the temperature and current of chaotic lasers with different TEC models. The range of the maximum output voltage at the TEC end is from 0 to 3.3 V. The output current stability is controlled within 0.02%, and the output wavelength fluctuation of the laser is stabilized within 9 pm. Compared with the control of the Newport driver, the normalized mean square error of the output wavelength of transmitter optical subassembly (TOSA) laser is decreased from 0.004 4 to 0.002 0. The stability of control has been improved.

High Assembly Tolerance and Cost-Effective 100-Gb/s TOSA With Silica-PLC AWG Multiplexer

A low-cost hybrid-integrated transmitter optical sub-assembly (TOSA) for a 100-Gb/s coarse wavelength division multiplexing (CWDM) transceiver with high assembly tolerance has been demonstrated. We have proposed a novel two-lens configuration for the coupling between distributed feedback laser diodes and a silica-based planar lightwave circuit arrayed waveguide grating to relax the lenses assembly requirement. For this TOSA, the 1-dB assembly tolerances of all lenses are over ±15 μ m. Furthermore, we use a flexible printed circuit to connect the interior and exterior of the TOSA for radiofrequency signal transmission instead of the conventional ceramic feed-through box. Finally, a TOSA was packaged with a size of 22 mm × 10.7 mm × 4.5 mm. Error-free transmission over a 10-km single-mode fiber was successfully achieved when all four lanes were driven simultaneously with a total bit rate of 4 × 25.78125 Gb/s at an operating temperature of 25 °C.

A TOSA/ROSA-based optical transmitter (MTx+)/transceiver (MTRx+) for high-energy physics experiments

We present a dual-channel optical transmitter (MTx+)/transceiver (MTRx+) for the front-end readout electronics of high-energy physics experiments. MTx+ utilizes two Transmitter Optical Sub-Assemblies (TOSAs) and MTRx+ utilizes a TOSA and a Receiver Optical Sub-Assemblies (ROSA). Both MTx+ and MTRx+ receive multimode fibers with standard Lucent Connectors (LCs) as the optical interface and can be panel or board mounted to a motherboard with a standard Enhanced Small Form-factor Pluggable (SFP+) connector as the electrical interface. MTx+ and MTRx+ employ a dual-channel Vertical-Cavity Surface-Emitting Laser (VCSEL) driver ASIC called LOCld65, which brings the transmitting data rate up to 14 Gbps per channel. MTx+ and MTRx+ have been tested to survive 4.9 kGy(SiO2).

1.3-µm 4×25-Gb/s hybrid integrated TOSA and ROSA

The design and fabrication of a compact and low-cost 4×25-Gb/s transmitter optical sub-assembly (TOSA) and receiver optical sub-assembly (ROSA) using a hybrid integrated technique are reported. TOSA and ROSA are developed without thermoelectric cooler for coarse wavelength division multiplexing applications. Physical dimension of the packaged optical subassembly is limited to 11.5 mm×5.4 mm×5.4 mm. The design of TOSA and ROSA is employed using a silica-based arrayed waveguide grating chip to select the specific channel wavelength at O-band. In TOSA, the wavelength of four 1.3-µm discrete directly modulated laser chips is well controlled based on the reconstruction equivalent chirp technique. In the back-to-back transmission test, bit error rates for all lanes of cascade of the TOSA and ROSA are small. A clear opening eye diagram is obtained.

200 Gb/s PAM-4 transmission over 10 km of standard single-mode fiber using multiwavelength directly modulated transmitter optical subassemblies for data center

A 200-Gb / s wavelength-division multiplexing transmission system using multiwavelength directly modulated transmitter optical subassemblies for data center has been proposed and demonstrated experimentally. The 8 × 25 Gb / s PAM-4 optical transmission system over 10 km of standard single-mode fiber is tested. The penalty variation within 1 dB for eight channels indicates that colorless transmission operation in the C-band is feasible with stable performance. Clear eye openings without any distortion show a good linearity characteristic for the optical transmission system. The advantages of integration, channelization, miniaturization, and low power consumption of the proposed scheme present a promising result for data center interconnection.

Monolithic integrated 4[formula omitted]25 Gb/s transmitter optical subassembly at 1.55 [formula omitted

We report a monolithic integrated 4×25 Gb/s transmitter optical subassembly (TOSA) module at 1.55 μm. The module consists of 4 directly modulated lasers (DMLs) and an arrayed waveguide grating (AWG) with 400 GHz channel spacing. The DMLs and AWG are highly integrated on a 4 mm×6 mm InP chip which is mounted on an AlN substrate and butterfly packaged. The characteristic of the TOSA module is measured in terms of optical spectra, crosstalk and small-signal frequency response. Data transmission propagating over 3.1 km single mode fiber (SMF) at 25 Gb/s with non-return to zero on–off keying (NRZ-OOK) modulation is explored experimentally. The results show an excellent uniformity of the 4 DMLs, which all reaches 25 Gb/s. The transmission rate up to 100 Gb/s for back-to-back (BTB) and 3.1 km fiber transmission with an error rate of 10−9 is reached. Of great importance, the packaged 4×25 Gb/s TOSA module meets the ITU standards very well, showing a promising extension on more channels and higher transmission speed

Efficient Optical Alignment Technique for Compact 100 and 400 GbE TOSAs With Integrated Multiplexing With Free Space Optics

An efficient and low-cost optical alignment technique is established for the first time for compact transmitter optical sub-assemblies (TOSAs) with an integrated multiplexer based on free space optics (FSO) for 100 and 400 Gbps Ethernet (GbE) applications. A compact FSO system for the 100 GbE TOSA is fabricated in a compact package 6.5 × 15.1 × 5.6 mm in size to confirm the validity of the technique. It is demonstrated by experiment that the optimum optical alignment condition can successfully be figured out by this technique without any expensive equipment, which has been a significant issue for TOSAs with integrated FSO systems, confirming the validity of the technique. Further, Monte Carlo simulations show that the optical output power distribution across the lanes is compatible with the 100 GbE LR4 specification, indicating the suitability of the proposed low-cost alignment technique. It is also shown that the acceptable long-term power variation required for reliability is predicted owing to the relaxation of the positional tolerance of the collimator lenses, which is obtained by the proposed technique. Finally the feasibility of the technique is discussed for 400 GbE TOSAs with eight-lane optical systems.

Power budget of 25-Gb/s digital orthogonal filter multiple access PONs with 10G-class optics

Abstract Power budget is a key factor that should be considered in intensity modulation and direct detection (IM/DD) passive optical networks (PONs). Based on the low-cost 10G-class electro-absorption modulated laser (EML) operating at C-band, we not only experimentally and theoretically investigate the interplay between the chromatic dispersion, the chirp of EML, and the self-phase modulation (SPM), but also explore the influences of the resolution and timing jitter of the analog to digital converter (ADC). Both theoretical and experimental results show that high power budget can be effectively achieved by making full use of the high launch power induced SPM effect and EML-induced frequency chirp. Based on the 10-G transmitter optical sub-assembly (TOSA) and receiver optical sub-assembly (ROSA), we successfully realize 25 Gb/s signal transmission at C-band over 25 km standard single mode fiber (SSMF) in IM/DD PON system. Even the worst performing bands can still achieve 25 dB power budget. The proposed scheme in this work has a potential application in future cost-effective optical access networks.