250 Mbit/s over 100 m SI-POF with RCLED source using integrated post-equaliser

Abstract

A high-speed transmission over step-index plastic optical fibre (SI-POF) using a resonant cavity light emitting diode (RCLED) is described. The integrated optical receiver is realised in 0.6 mm BiCMOS technology with an integrated large-area Si photodiode. The design consists of a TIA, equaliser and post-amplifier stage followed by a 50 V output driver. The integrated equaliser can be adapted via an external control voltage to different SI-POF lengths and RCLED limited bandwidths. A data rate of 250 Mbit/s can be transmitted over a 50 m-long SI-POF with a sensitivity of 222dBm at BER of 10 29 and over a 100 m-long SI-POF with a sensitivity of 224 dBm at a BER of 10 26 .Introduction: Poly-methylmetacrylate (PMMA) step-index plastic optical fibre (SI-POF) is very interesting in several applications (industrial automation, automotive, home networking) where it shows key advantages over the more traditional copper cabling. PMMA SI-POF has a low bandwidth of 60 MHz/100 m which limits the maximum binary data rate (DR) which can be transmitted to less than 100 Mbit/ s over 100 m POF length [1].Owing to their large area, LEDs cannot be modulated typically above 100 Mbit/s. The coupling loss to POF is high owing to the wide emission angle (508). LEDs are cheap and simple to use. Resonant cavity light emitting diode (RCLEDs) are different from conventional LEDs due to the two additional Bragg mirrors above and below the light generation layer. Nowadays, RCLEDs are available in the 650 nm wavelength range. Due to the RCLEDs' special design they allow higher modulation speed (250 Mbit/s) than LEDs [2]. RCLEDs have a better temperature performance than laser diodes (LDs) and vertical cavity surface emitting lasers (VCSELs). The RCLED operates up to 858C whereas the maximum operating temperature for red VCSELs is 508C. RCLEDs do not have a threshold current so a simple driver circuit can be used whereas LDs need sophisticated drivers for current control [1,3]. The main limiting factor in RCLED applications for POF is its bandwidth (BW , 175MHz) which is higher than LEDs' but smaller than LD's bandwidth. The pre-equalisation and optimisation of a RCLED driver can increase the RCLED data rate to 1 Gbit/s [4].The problem of the limited bandwidth of the SI-POF and RCLED system can be overcome by using complex modulation formats like multilevel pulse amplitude modulation (M-PAM) [3,5]. 300 Mbit/s over a 50 m-long POF link using a commercial RCLED at BER 1.9 × 10 23 was presented in [5] using carrier-less amplitude phase modulation. There is a need for more circuits at the transmitter to generate these complex modulation formats and also at the receiver to decode these complex signals to binary [6,7]. Post-equalisation techniques can help to solve the problem of limited bandwidth of the SI-POF [8]. Binary signalling equalisation is a preferable solution for a cheap POF optical receiver system with less complexity and lower power consumption. The approach is to use a binary signal and an integrated post-equaliser to compensate for th...

500 MBIT/s OOK‐NRZ transceiver for 50 m GI‐POF using 100 MHz RC‐led

“…As indicated in previous works [2,5], there is a trade-off between total integrated noise and intersymbol interference in the wide band TIA design. These performances can be evaluated from eye diagrams of the output of the TIA by eye closure and jitter situations.…”

“…Various process technologies can be adopted to implement TIAs, in which the CMOS process technology benefits from its low power, low cost, and easy integration with other circuits. Recently, researches on CMOS TIAs have been successfully proposed [2][3][4][5][6]. Generally, performances of TIAs are mainly considered by the 3-dB bandwidth and the transimpedance gain.…”

“…For a conventional TIA, the bandwidth is limited by the large PD capacitance and parasitic capacitances at the input termination. The RGC technique has been proposed to alleviate the input bandwidth restriction [5,6]. The input impedance of a RGC is small and suitable for first stage of the TIA.…”

“…One remaining problem for POF‐LED systems is the low modulation bandwidth of LED, which limits its on‐off keying (OOK) modulation rate at 250 Mbit/s . Basically, LED's modulation bandwidth can be improved by miniaturizing or heavily doping the active region.…”

A 622 Mbit/s transmitter for POF-based home networks using red LED

“…Although on-off keying (OOK) modulation has low spectral efficiency, it is the simplest modulation scheme for low cost transmitter design. So far, there have been several demonstra tions for POF-LED systems using OOK modulation [5]- [8].…”