A Record 1-km MMF NRZ 25.78-Gb/s Error-Free Link Using a 1060-nm DIC VCSEL

We report successful achievement of a record long distance error-free transmission of 1000-m 50- $\mu \text{m}$ -core multi-mode fiber (MMF) in a non-return-to-zero 25.78-Gb/s modulated vertical cavity surface emitting laser-based optical link using four-channel miniature parallel-optical modules. The optical power is centralized within the core of MMF by an active alignment assembly. The restricted launch condition gives a very high effective modal bandwidth (EMB) of >9 GHz $\cdot $ km based on the calculations and the required performance data specified in TIA-FOTP-220. An EMB of 11.5 GHz $\cdot $ km provides a very good agreement between the calculated and measured power penalty characteristics. Such a long distance low-cost MMF link, operating at 1060-nm wavelength is potentially an alternative solution to PSM4.

I. Introduction

The demand of long distance transmission in short reach applications has been growing to cover large scale data centers. For such long distance 100 GbE solutions, the multi-source agreement (MSA) for the parallel single-mode four-lane (PSM4) using a particular small form factor was generated to cover the specified distance of 2-500 m [1]. The usage of single-mode fibers (SMFs) with optical signals launched from a light source emitted at the specified wavelength range between 1295 nm and 1325 nm is useful to realize long distance signal transmission. However, the optical coupling between a vertical cavity surface emitting laser (VCSEL) array and a multi-lane SMF cable requires very precise alignment in the assembly process. Also, such a SMF-based multi-lane high-density optical connectivity is challenging in terms of manufacturing precision-molded parts required in mass production and hence it likely would result in a higher price. On the other hand, several error-free demonstrations in long distance links using multi-mode fiber (MMF) have been reported. For non-return-to-zero (NRZ) modulated around the Ethernet base rate of 25.78 Gb/s at the bit error rate (BER) of , 850-nm VCSEL-based 25-Gb/s signal transmission in an OM4 fiber of 500 m was reported with the usage of a chromatic dispersion compensation MMF jumper [2]. 25-Gb/s 820-m signal transmission in a specialized MMF for 1310 nm was demonstrated as the best record of long distance [3], where the chromatic dispersion can be zero ideally. As a similar approach for a low chromatic dispersion, we have proposed to use the 1060-nm VCSELs for such MMF links. In our previous work, we demonstrated 1060-nm VCSEL-based 10-Gb/s 1-km signal transmission using a specialized MMF which maximizes an effective modal bandwidth (EMB) at 1060 nm [4], 500-m 25.78-Gb/s transmission in an OM4 fiber with a modal dispersion compensation fiber [5], and 500-m 28-Gb/s transmission in a 1060-nm specialized MMF [6]. In any case, modal dispersion is the dominant factor that limits the achievable distance, and the EMB depends on the dispersion mode delay (DMD) of the MMF and the launch condition. In this letter, we investigate the optimum conditions for maximizing the EMB of a 1060-nm specialized MMF and error-free transmission distance based on the high-speed 1060-nm VCSEL.