Yi-Cheng Li

Optical 16-QAM-52-OFDM transmission at 4 Gbit/s by directly modulating a coherently injection-locked colorless laser diode

Coherently injection-locked and directly modulated weak-resonant-cavity laser diode (WRC-FPLD) for back-to-back optical 16-quadrature-amplitude-modulation (QAM) and 52-subcarrier orthogonal frequency division multiplexing (OFDM) transmission with maximum bit rate up to 4 Gbit/s at carrier frequency of 2.5 GHz is demonstrated. The WRC-FPLD transmitter source is a specific design with very weak-resonant longitudinal modes to preserve its broadband gain spectral characteristics for serving as a colorless WDM-PON transmitter. Under coherent injection-locking, the relative-intensity noise (RIN) of the injection-locked WRC-FPLD can be suppressed to ?105 dBc/Hz and the error vector magnitude of the received optical OFDM data is greatly reduced with the amplitude error suppressed down 5.5%. Such a coherently injection-locked single-mode WRC-FPLD can perform both the back-to-back and the 25-km-SMF 16-QAM-52-OFDM transmissions with a symbol rate of 20-MSa/s in each OFDM subcarrier. After coherent injection locking, the BER of the back-to-back transmitted 16-QAM-52-OFDM data is reduced to 2.5 × 10(-5) at receiving power of ?10 dBm. After propagating along a 25-km-long SMF, a receiving power sensitivity of ?7.5 dBm is required to obtain a lowest BER of 2.5 × 10(-5), and a power penalty of 2.7 dB is observed when comparing with the back-to-back transmission.

Suppressing the relaxation oscillation noise of injection-locked WRC-FPLD for directly modulated OFDM transmission

By up-shifting the relaxation oscillation peak and suppressing its relative intensity noise in a weak-resonant-cavity Fabry-Perot laser diode (WRC-FPLD) under intense injection-locking, the directly modulated transmission of optical 16 quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) data-stream is demonstrated. The total bit rate of up to 20 Gbit/s within 5-GHz bandwidth is achieved by using the OFDM subcarrier pre-leveling technique. With increasing the injection-locking power from -12 to -3 dBm, the effective reduction on threshold current of the WRC-FPLD significantly shifts its relaxation oscillation frequency from 5 to 7.5 GHz. This concurrently induces an up-shift of the peak relative intensity noise (RIN) of the WRC-FPLD, and effectively suppresses the background RIN level to -104 dBc/Hz within the OFDM band between 3 and 6 GHz. The enhanced signal-to-noise ratio from 16 to 20 dB leads to a significant reduction of bit-error-rate (BER) of the back-to-back transmitted 16-QAM-OFDM data from 1.3 × 10(-3) to 5 × 10(-5), which slightly degrades to 1.1 × 10(-4) after 25-km single-mode fiber (SMF) transmission. However, the enlarged injection-locking power from -12 to -3 dBm inevitably declines the modulation throughput and increases its negative throughput slope from -0.8 to -1.9 dBm/GHz. After pre-leveling the peak amplitude of the OFDM subcarriers to compensate the throughput degradation of the directly modulated WRC-FPLD, the BER under 25-km SMF transmission can be further improved to 3 × 10(-5) under a receiving power of -3 dBm.

10-Gbit/s direct modulation of a TO-56-can packed 600-μm long laser diode with 2% front-facet reflectance

A 600-μm long-cavity laser diode with a front-facet reflectance of 2% is demonstrated as a colorless OC-192 transmitter for the future DWDM-PON, which is packed in a TO-56-can package of only 4-GHz frequency bandwidth but can be over-bandwidth modulated with 10-Gbit/s non-return-to-zero data-stream. The coherent injection-locking successfully suppresses its side-mode intensity and noise floor level, which further improves its modulation throughput at higher frequencies. With increasing the coherent injection-locking power from -12 to -3 dBm, the side-mode suppression ratio significantly increases from 39 to 50 dB, which also suppresses the frequency chirp from -12 to -4 GHz within a temporal range of 150 ps. The dense but weak longitudinal modes (with 0.6-nm spacing) in the long-cavity laser diode suppresses to one single-mode in a 100-GHz wide DWDM channel for carrying the OC-192 data at 9.953 Gbit/s. Such an over-bandwidth modulated laser diode still exhibits an on/off extinction ratio of 6.68 dB and a signal-to-noise ratio of 4.96 dB, which can provide a back-to-back receiving power sensitivity of -12.2 dBm at BER of 10⁻⁹. After 25-km DSF transmission of the OOK data-stream at a bit rate up to 10 Gbit/s, the receiving power sensitivity is -10.1 dBm at a requested BER of 10⁻⁹.

Using a L-Band Weak-Resonant-Cavity FPLD for Subcarrier Amplitude Pre-Leveled 16-QAM-OFDM Transmission at 20 Gbit/s

A directly modulated and coherently injection-locked WRC-FPLD transmitter is preliminarily employed to perform the 16-QAM-OFDM data transmission by using an OFDM subcarrier amplitude pre-leveling technique. The maximum transmission bit-rate of 20-Gbit/s is reported by fusing the OFDM subcarrier pre-leveling with the coherent injection-locking techniques in such a directly modulated WRC-FPLD. Without pre-leveling the OFDM subcarrier, the coherently injection-locked L-band WRC-FPLD suppresses its mode-partition noise to improve the EVM of the 16-QAM-OFDM data only from 13.52% to 10.2%. The OFDM subcarrier pre-leveling effectively compensate the finite bandwidth and unflattened modulating response of the injection-locked WRC-FPLD to improve the transmission EVM and SNR performances. The received constellation plot reveals that the EVM and SNR of the back-to-back transmitted 16-QAM-OFDM data are significantly improved to 5.58% and 17 dB, respectively. With the use of both injection-locking and pre-leveling techniques, the directly 16-QAM-OFDM modulated WRC-FPLD transmitter can reach the FEC limited BER of 3.8 × 10-3 at a receiving power sensitivity of -10 dBm. The OFDM subcarrier pre-leveling technique helps the WRC-FPLD to reduce the overall BER of 16-QAM-OFDM data by one order of magnitude, providing a minimum BER of 4.5 × 10-5 at a receiving power of -2 dBm.

20-Gbps WDM-PON transmissions employing weak-resonant-cavity FPLD with OFDM and SC-FDE modulation formats

We experimentally demonstrate a superior performance of 20-Gbps OFDM/SC-FDE transmission over 20-km WDM-PONs, using a channelized weak-resonant-cavity FPLD with a modulation bandwidth of only 1.25 GHz by using injection-locking, direct detection and adopting the power-loading algorithm.

Specific Jacket SMA-Connected TO-Can Package FPLD Transmitter With Direct Modulation Bandwidth Beyond 6 GHz for 256-QAM Single or Multisubcarrier OOFDM up to 15 Gb/s

A specifically designed SMA connector with jacket signal pin configuration is used to connect the transistor outline can (TO-can) packaged Fabry-Pérot laser diode (FPLD) for enhancing its direct modulation bandwidth beyond 6 GHz. The direct modulation of such an TO-can/jacket-SMA packaged FPLD with a 256 quadrature amplitude modulation (QAM) and single subcarrier optical orthogonal frequency-division multiplexing (OOFDM) format data stream at carrier frequency up to 6 GHz is approached with 10 MSa/s symbol rate. The optimized 256-QAM data with error vector magnitude (EVM) of 1.5% and signal-to-noise ratio (SNR) of 32.5 dB are observed, corresponding to a bit error rate as low as 1.1 × 10-6 and a highest carrier-to-noise ratio of 43.5 dB. Under injection locking, the tradeoff between the lengthened photon lifetime and the enlarged threshold current reduction of such an M-QAM-N-OOFDM modulated FPLD is theoretically and experimentally investigated to explain the saturation of SNR at 31.5 dB and EVM at 1.7%. Both 16-QAM and 64-QAM 200-subcarrier OOFDM formats with total transmission bit rates up to 15.6 and 23.4 Gb/s, respectively, are performed at carrier frequency of 2 GHz. The corresponding EVM and SNR for the 16-QAM OOFDM are determined as 11.67% and 20 dB, respectively. Under 64-QAM and 200-subcarrier OOFDM modulation, the received data stream shows a slightly degraded EVM and SNR of 12.85% and 19 dB, respectively.

Coherently wavelength injection-locking a 600-μm long cavity colorless laser diode for 16-QAM OFDM at 12 Gbit/s over 25-km SMF

The coherent injection-locking and directly modulation of a long-cavity colorless laser diode with 1% end-facet reflectance and weak-resonant longitudinal modes is employed as an universal optical transmitter to demonstrated for optical 16-QAM OFDM transmission at 12 Gbit/s over 25 km in a DWDM-PON system. The optimized bias current of 30 mA (~1.5Ith) with corresponding extinction ratio (ER) of 6 dB and the external injection power of -9 dBm is (are) required for such a wavelength-locked universal transmitter to carry the 16-QAM and 122-subcarrier formatted OFDM and data-stream. By increasing external injection-locking from -9 dBm to 0 dBm, the peak-to-peak chirp of the OFDM data stream reduces from 7.7 to 5.4 GHz. The side mode suppression ratio (SMSR) of up to 50 dB is achieved with wider detuning range between -0.5 nm to 2.0 nm under an injection power of 0 dBm. By modulating such a colorless laser diode with an OFDM data stream of 122 subcarriers at a central carrier frequency of 1.5625 GHz and a total bandwidth of 3 GHz, the transmission data rate of up to 12 Gbit/s in standard single-mode fiber over 25 km is demonstrated to achieve an error vector magnitude (EVM) of 5.435%. Such a universal colorless DWDM-PON transmitter can deliver the optical OFDM data-stream at 12 Gbit/s QAM-OFDM data after 25-km transmission with a receiving power sensitivity of -7 dBm at BER of 3.6 × 10(-7) when pre-amplifying the OFDM data by 5 dB.

An Injection-Locked Weak-Resonant-Cavity Laser Diode for Beyond-Bandwidth Encoded 10-Gb/s OOK Transmission

A coherently injection-locked and beyond-bandwidth-modulated weak-resonant-cavity laser diode (WRC-FPLD) transmitter packaged by a conventional TO-56 can package for an upstream 10-Gb/s OOK transmission is demonstrated in a DWDM-PON. With specific temperature controlling, the WRC-FPLD is able to maintain its temperature during the process of injection locking. Based on the theoretical analysis of modified rate equations, the injection-locked WRC-FPLD exhibits not only a broadband gain spectrum but also a large modulation bandwidth. Successfully implementing injection locking enhances the high-frequency throughput response but inevitably impairs the throughput intensity at a low-frequency region. By properly increasing the injection-locking power, the modulation bandwidth of the injection-locked WRC-FPLD can be further improved. In addition, the extinction ratio and the signal-to-noise ratio (SNR) of the transmitted 10-Gb/s NRZ-OOK data can also be improved from 5.58 to 6.95 dB and from 5.43 to 6.18, respectively, by increasing the injection-locking power from -12 to -3 dBm, which improves the receiving power sensitivity by 1.6 dB. The optimized receiving power sensitivity at a requested bit error rate (BER) of 10-9 is -15.4 dBm by setting the injection-locking power at -3 dBm. After a 25-km transmission, such an overbandwidth-modulated and injection-locked WRC-FPLD reveals a receiving power sensitivity of -11.6 dBm at the same BER of 10-9.

Directly modulating a long weak-resonant-cavity laser diode at limited bandwidth of 5 GHz with pre-leveled 16-QAM OFDM transmission at 20 Gbit/s

Coherently injection-locked and directly modulated long weak-resonant-cavity FPLD for pre-leveled optical 16-QAM OFDM transmission in DWDM-PON at 20.25-Gbit/s over 25-km is demonstrated with receiving sensitivity of -8dBm at EVM of 8% and BER of 3.8×10-3.

Reusing Downstream Carrier in Colorless Laser Diode for Full-Duplex 64-QAM OFDM

Without the need of any inline data eraser, the downstream carrier is reused in an upstream colorless laser diode transmitter to demonstrate full-duplex bidirectional 64-QAM OFDM passive optical network (PON) at up to 18 Gb/s. Therein, the downstream signal is used to control the wavelength of upstream laser diode by injection locking, and the slave laser diode then generates the injection-locked carrier for carrying the upstream signal. Distributing the OFDM subcarriers into dual frequency regions for upstream (baseband at 0-3 GHz) and downstream (up-shifted band at 3-6 GHz) transmissions avoids the crosstalk and simplifies the full-duplex system. The downstream power splitting ratio of 60/40 is optimized for receiving/injection branches at user end. For the downstream 64-QAM OFDM data after propagating 25-km SMF, a sensitivity of received power at least -8.5 dBm is required to suppress the BER below 3.8 × 10-3 for the forward-error correction (FEC) criterion. When directly reusing the downstream carrier with unerased data to injection-lock the colorless laser diode, the 25-km SMF transmitted upstream 64-QAM OFDM data exhibits an SNR of 22.9 dB and an error vector magnitude of 4.1%, which provides a BER of 1.5 × 10-3 at a received power of -5.8 dBm. Such a downstream carrier reused colorless laser diode upstream transmitter with inline eraser-free operation has shown its applicability for full-duplex quadrature amplitude modulation orthogonal frequency-division multiplexing PON.