Min-Chi Cheng

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.

Direct QAM-OFDM Encoding of an L-band Master-to-Slave Injection-Locked WRC-FPLD Pair for 28 × 20 Gb/s DWDM-PON Transmission

The 560 Gb/s (20 Gb/s × 28 channels) DWDM-PON with 16 quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) transmission over 25-km SMF by using the master-to-slave injection-locked weak-resonant-cavity Fabry-Perot laser diode (WRC-FPLD) pair is demonstrated. After master-to-slave injection-locking, the BER of the 16-QAM OFDM data stream under back-to-back and 25-km transmissions can be improved from 3.3 × 10-3 to 2.1 × 10-5 and from 1.4 × 10-1 to 1.2 × 10-3, respectively. With OFDM subcarrier pre-leveling, the BER of 16-QAM OFDM data transmitted by the master-to-slave injection-locked WRC-FPLD over 25-km transmission is further improved from 1.2 × 10-3 to 2.1 × 10-4, concurrently enabling the 28 channel transmissions at 20 Gb/s with BER below FEC-limit of 3.8 × 10-3. The back-to-back transmission of pre-leveled 64-QAM OFDM data at 30 Gb/s under is also demonstrated to achieve FEC limited BER at receiving power of -6 dBm by using the main of the master-to-slave injection-locked slave WRC-FPLD. The partially coherent injection-locking of maser-to-slave WRC-FPLD pair is comparable with the coherent DFB injection-locked WRC-FPLD, which is capable of serving as the universal transmitters with competitive performance of a power penalty as low as 0.5 dB between WRC-FPLD-to-WRC-FPLD and DFB-to-WRC-FPLD.

A Novel Colorless FPLD Packaged With TO-Can for 30-Gbit/s Preamplified 64-QAM-OFDM Transmission

A colorless FPLD directly modulated by the preamplified 64-QAM-OFDM at 30 Gbit/s is demonstrated with suppressed intensity noise and modulation distortion due to the enhanced signal-to-noise ratio (SNR) and reduced frequency chirp. To encode the colorless FPLD with 90% modulation depth when up shifting the dc bias to 2.5 times threshold of the colorless FPLD under injection-locking at 3 dBm, the preamplification of the electrical 64-QAM-OFDM data achieves the least SNR degradation and maintains data extinction. With the 64-QAM-OFDM subcarrier amplitude preleveled and preamplified encoding procedure, the colorless FPLD effectively promotes high on/off data extinction by suppressing the throughput power declination to <;5 dB and reducing the power-to-frequency slope to -0.7 dB/GHz within 5-GHz modulation bandwidth. The received bit-error-rate (BER) contour map of the preamplified 64-QAM-OFDM data carried by the colorless FPLD achieves its minimum of <;2.0 × 10-3 and reveals large tolerances to the injection power and the biasing level. After preleveling the amplitude slope of the OFDM subcarriers, the error vector magnitude reduces to 8.6% and the SNR enhances to 21.2dB even after 25-km SMF transmission. The colorless FPLD encoded by preamplified and preleveled 64-QAM-OFDM data apparently optimizes both back-to-back and 25-km transmissions with corresponding BERs minimized to 1.1 × 10-3 and 3.5 × 10-3, 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.

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.

TO-56-can packaged colorless WRC-FPLD for QAM OFDM transmission at 42 Gbit/s over 25-km SMF

The weak-resonant-cavity Fabry-Perot laser diode (WRC-FPLD) with colorless and channelized mode features is a new-class optical transmitter fulfilling the need of next-generation communications. By packaging the colorless WRC-FPLD transmitter with a 10-GHz transistor-outline-56-can (TO-56-can), the premier demonstration on directly modulated 42-Gbit/s/channel quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) transmission is demonstrated via wavelength injection-locking. Enlarging the injection level effectively up-shifts the relaxation oscillation peak and suppresses the relative intensity noise, which facilitates the TO-56-can packaged WRC-FPLD to improve its modulation throughput bandwidth to 9 GHz and enhance its signal-to-noise ratio to 22 dB. By pre-amplifying the directly modulated QAM-OFDM data with a total raw bit rate of 42 Gbit/s, the receiving bit-error-rate (BER) under back-to-back transmission can be reduced below the forward-error-correction (FEC) limited BER of 3.8 × 10(-3). Such a colorless WRC-FPLD enables the QAM-OFDM transmission over a 25-km long single-mode-fiber based metropolitan access network with its BER matching the FEC criterion at a receiving power of -2 dBm.

Master-to-slave injection-locked WRC-FPLD for multi-QAM-OFDM transmission

A master-to-slave injection-locked weak-resonant-cavity FPLD directly modulated by 16 quadrature amplitude modulation (QAM) orthogonal frequency division multiplexing (OFDM) is demonstrated for DWDM-OFDM-PON transmission. By up-shifting the relaxation oscillation peak and suppressing the relative intensity noise of the WRC-FPLD under partially coherent injection-locking, the maser-to-slave WRC-FPLD pair shows comparable transmission performance with the coherently injection-locked WRC-FPLD by DFBLD, which is capable of serving as the universal transmitters in next-generation DWDM-PON.

A Directly Modulated Colorless Laser Diode for the M-ary-QAM OFDM Transmission

The M-ary-QAM OFDM transmission by using a directly modulated colorless laser diode with its noise suppressed and wavelength controlled by the external injection is demonstrated with a BER of <3.8×10⁻³ after the 25-km transmission.