H. K. Shim

25-Gb/s TDM Optical Link Using EMLs for Mobile Fronthaul Network of LTE-A System

We propose and demonstrate a common public radio interface (CPRI)-compliant 25.2923-Gb/s mobile fronthaul network for long term evolution-advanced (LTE-A) systems. In order to meet the CPRI specifications and the stringent latency requirement of the LTE-A fronthaul network cost-effectively, we use the synchronous time-division-multiplexing, forward-error correction, and electrical equalization techniques. To enhance the cost-effectiveness, we also use an electroabsorption-modulated laser and exploit the possibility of using simple modulation formats such as the ON-OFF keying, electrical duobinary, and four-level pulse amplitude modulation. The performance of the proposed network is evaluated experimentally in terms of the tolerances to fiber dispersion and optical reflection.

Practical 12.5-Gb/s, 12.5-GHz spaced ultra-dense WDM PON

We report a practical 12.5-Gb/s, 12.5-GHz-spaced ultra-dense wavelength-division-multiplexed passive optical network (UD-WDM PON). For the cost-effectiveness, we implement the downstream links by using electro-absorption modulated lasers (EMLs) in the 4-level pulse amplitude modulation (4PAM) format and PIN receivers, and the upstream links by using reflective semiconductor optical amplifiers (RSOAs) modulated in the quadrature phase-shift-keying (QPSK) format and low-cost self-homodyne receivers. To further enhance its cost-effectiveness, we also utilize an optical frequency comb generator, instead of a large number of wavelength-selected lasers, to provide the seed light for these colorless RSOAs. We optimize the operating conditions of the EMLs and RSOAs to maximize the power margins in the presence of the crosstalk arising from closely spaced neighboring channels and the inter-symbol interference (ISI) caused by the narrow passband of the cascaded arrayed-waveguide gratings (AWGs) as well as the limited modulation bandwidths of RSOAs. The experimental results show that we can secure the power margins of >2.5 dB for both upstream and downstream links of the proposed UD-WDM PON.

Transmission of 40-Gb/s QPSK upstream signal in RSOA-based coherent WDM PON using offset PDM technique

We demonstrate the 40-Gb/s upstream transmission in the 60-km reach wavelength-division-multiplexed passive optical network (WDM PON) implemented by using directly modulated reflective semiconductor optical amplifiers (RSOAs) and self-homodyne receivers. It is difficult to operate the RSOA at 40 Gb/s due to its limited modulation bandwidth. To overcome this problem and generate 40-Gb/s upstream signal, we utilize the quadrature phase-shift-keying (QPSK) format and the offset polarization-division-multiplexing (PDM) technique. For this purpose, we install two RSOAs at each ONU and provide the seed light for these RSOAs by polarization-multiplexing the outputs of two lasers with a small frequency offset (20 GHz). This frequency offset is used to separate the polarization-multiplexed seed light by using a simple delay-line interferometer (DLI), instead of the polarization-beam splitter and polarization controller, at the ONU. The separated seed light is modulated by each RSOA at 20 Gb/s in the QPSK format, and then combined again by the DLI before sent back to the central office (CO). The results show that this WDM PON can support the transmission of 40-Gb/s channels spaced at 50 GHz over 60 km without using any remote optical amplifiers.

Correlation-based OTDR for in-service monitoring of 64-split TDM PON

We demonstrate a correlation-based OTDR for the in-service monitoring of the 64-split TDM PON. For this purpose, we improve its dynamic range by using the pseudo-random noise sequence superimposed on the data signal.

Demonstration of 40-Gb/s QPSK upstream transmission in long-reach RSOA-based coherent WDM PON using offset PDM technique

We demonstrate the 40-Gb/s QPSK upstream transmission in 60-km reach WDM PON (channel spacing: 50 GHz) implemented by using directly modulated RSOAs and self-homodyne receivers together with the offset PDM technique.

20-Gb/s operation of RSOA using polar return-to-zero 4-PAM modulation format and direct detection

We demonstrate the upstream transmission of 20-Gb/s polar RZ 4-PAM signal over 20 km of loopback SSMF link by using a directly-modulated RSOA and a direct-detection receiver.

25.2923-Gb/s optical link using EML for mobile fronthaul network of LTE-A systems

We demonstrate a CPRI-based 25.2923-Gb/s optical link by using an electro-absorption modulated laser (EML) for the fronthaul network of LTE-A systems. We modulate the EML in OOK, electrical duobinary, and 4-PAM formats, and evaluate their performances for the fiber dispersion and optical reflections.