Yu-Chuan Su

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 Self-Feedback Controlled Colorless Fabry-Perot Laser Diode for Remote Control Free Single-Mode DWDM-PON Transmission

A remote-control-free self-feedback colorless Fabry-Perot laser diode (FPLD) transmitter single-mode controlled with a fiber Bragg grating reflector-based self-feedback block is successfully demonstrated and optimized for 2.5-5 Gb/s dense wavelength division multiplexed passive optical network transmissions. The maximal power budget of such a single-mode lasing colorless FPLD at 2.5-Gb/s transmission is determined as 25 dB under the feedback ratio of 90%. With increasing the bias of the self-feedback colorless FPLD, both the power of self-feedback carrier and extinction of the inherent modes are enhanced. Between the bias of 38 and 42 mA (~2-2.25 times of Ith), the tradeoff between injection efficiency and mode extinction is compromised, leading to the optimized single-mode output with side-mode suppression ratio of 48 dB, modal linewidth of 0.01 nm, and relative intensity noise floor of -102 dBc/Hz. At same bias, the self-feedback colorless FPLD modulated at 2.5-Gb/s can perform a 25-km single-mode fiber (SMF) transmission with a receiving power sensitivity of -30.5 dBm at bit error rate of 10-9. With the aid of a gain-saturated SOA fiber loop inserted in the self-feedback block to enhance the data-erasing, the self-feedback single-mode colorless FPLD successfully provides an error-free transmission up to 5 Gb/s after 25-km SMF.

Coherent Injection-Locking of Long-Cavity Colorless Laser Diodes With Low Front-Facet Reflectance for DWDM-PON Transmission

Long-cavity colorless laser diodes with different front-facet antireflection (AR) coatings are employed to perform the wavelength injection-locked ON-OFF-keying (OOK) data transmission. By changing front-facet reflectance of laser diode from 0.2% to 1.2%, the received OOK data enhance its Q factor by 6.3% and reduces its bit error rate (BER) by more than two orders of magnitude, which benefits from the improved signal-to-noise ratio and extinction ratio by up to 8.0%. Enlarging the injection-locking power from -6 to -3 dBm essentially helps the long-cavity colorless laser diode to promote its receiving power sensitivity from -27.9 to -29.2 dBm at BER of 10-9. However, the similar device with lower AR reflectance shows an opposite trend. The injection-locking-induced enhancement is limited within a frequency region controlled by the injection power, which results from a large disparity between continuous-wave injection and stimulated emission inside the long-cavity colorless laser diode. At same biased current and front-facet reflectance, a higher injection level provides a larger modulation throughput at a cost of decreasing bandwidth. The overinjection causes a limitation on frequency bandwidth of the long-cavity colorless laser diodes with lower front-facet reflectance. The numerical simulations with modified rate equations for the injection-locked long-cavity colorless laser diode with lower front-facet reflectance also elucidate that the transmission degrades distinctly at larger injection powers.

All Colorless FPLD-Based Bidirectional Full-Duplex DWDM-PON

All colorless Fabry-Perot laser diodes (FPLDs) with master-to-slave injection-locking and carrier-reusing are employed as down- and up-stream transmitters to demonstrate the bidirectionally 10-Gbit/s full-duplex on-off-keying transmission in a dense wavelength-division-multiplexed passive optical network system without using any high-coherent transmitter. By simply injecting the down-stream optical carrier into the up-stream slave colorless FPLD, the residual down-stream data can be greatly suppressed with a penalty on the relative intensity noise by only 2-4 dB. This facilitates a compact carrier-reusing without the need of additional data-eraser or injection master. Such a broadband colorless FPLD master can essentially make the down-stream slave approaching an error-free transmission after transmitting over 25-km MetroCor fiber at a receiving power of <;-13.5 dBm. By reusing the down-stream carrier with its data in-situ erased by the up-stream colorless FPLD itself, the single-mode injection-locked up-stream slave can also implement an error-free transmission after propagating over 25 km, providing a receiving power sensitivity of <;-9 dBm with a power penalty of 2 dB as compared to the back-to-back case.

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.

Data Erasing and Rewriting Capabilities of a Colorless FPLD Based Carrier-Reusing Transmitter

The inherent data-erasing functionality of a 10-Gb/s colorless Fabry-Pérot laser diode (FPLD) wavelength controlled by reusing a downstream optical carrier with encoded data is explored. By operating the injection-locked colorless FPLD at high dc bias, the unique in situ data-erasing mechanism is attributed to the almost identical power-to-current slope, regardless of optical injection-locking level. When reusing the downstream carrier, the injection-locked upstream colorless FPLD can significantly suppress the extinction ratio of the residual 10-Gb/s downstream data from 7.1 to <; 1 dB. This facilitates direct reuse of the downstream carrier without the need for an additional data eraser. With the data-erasing capability under 0-dBm injection, the carrier-reused upstream transmission successfully delivers on-off keying data up to 10 Gb/s with a signal-to-noise ratio of 6.2 dB and an extinction ratio of 5.4 dB. Even with a downstream injection power value of only -9 dBm, the upstream bit error rate (BER) of such a dual functional colorless FPLD biased at ≥2Ith indicates a BER of <; 1 × 10-10. This releases the typical demand on high power budget requested for downstream data transmission and carrier reusing. The large parametric tolerances of such a data-erasable and carrier-reusable colorless FPLD transmitter also facilitate its practical application in dense-wavelength-division multiplexed passive optical networks.

Multi-order bunched soliton pulse generation by nonlinear polarization rotation mode-locking erbium-doped fiber lasers with weak or strong polarization-dependent loss

With the assistance of weak or strong polarization-dependent loss (PDL) in the cavity, nonlinear polarization rotation mode-locking (NPRML) of an erbium-doped fiber laser (EDFL) is demonstrated to show transformation on the soliton from a single to multiple bunched state with nearly one order of magnitude variation on pulsewidth. With the bent intracavity fiber providing the weak PDL, the NPRML shortens the pulsewidth from only 5.3 ps to 4.9 ps and correspondingly broadens the spectral linewidth from 0.43 nm to 0.56 nm when enlarging the pump power from 100 mW to 325 mW. With the use of an inserted polarizer providing strong PDL in an EDFL, the fundamental soliton pulsewidth is significantly compressed to 390 fs, with the spectral linewidth as wide as 7.14 nm. In particular, the parameters of the soliton pulses are nearly unchanged at different pump powers; however, the soliton pulses split to form tightly bunched pulses circulating in the EDFL cavity. There are as many as 18 solitons tightly bunched together at the maximum pump power of up to 325 mW. Such a tightly bunched package can be elucidated by soliton energy quantization and long-range soliton interaction according to the perturbation theory in a passively mode-locked EDFL.

Colorless Laser Diodes for DWDM-PON Transmission

Since the requirement on data transmission capacity of the broadband internet access network is persistently increasing, the remarkable efforts have been paid on both optical wavelength and electrical frequency usages of the data transmitters emerged for developing the next-generation passive optical network (NGPON).

Effect of Injection Coherence on Noise and Bandwidth of Long-Cavity Colorless Laser Diode for Digital Modulation and Transmission

The weak-resonant-cavity Fabry-Perot laser diode (WRC-FPLD) injection-locked by three master sources with different degrees of coherence and directly modulated by two different digital modulation formats is demonstrated. The injection master coherence shows impact on noise, bandwidth, and modulation performances of the slave WRC-FPLD transmitter. Using the highly coherent master, the injection-locked WRC-FPLD reduces its relative intensity noise peak at 5 GHz by 18 dB and increases its throughput frequency response by 5 dB. This enables the error-free ON-OFF keying (OOK) transmission at 10 Gb/s with a required receiving power sensitivity of -15 dBm at an error rate of 10-9. The eye diagrams simulated from the modified rate equations are also performed to show such improvements. With highly coherent injection-locking, the transmitted error of the WRC-FPLD carried orthogonal frequency division multiplexing (OFDM) data with a modulation bandwidth of 3.1 GHz can be minimized to 1.6 × 10-13. In comparison, the master-to-slave injection-locked WPC-FPLD with partial coherence can also provide an 8-Gb/s OOK transmission with a receiving power sensitivity of -19 dBm at bit-error-rate (BER) of 109. Such a cost-effective colorless source also supports a 16-quadrature-amplitude modulation OFDM transmission at 12.5 Gb/s with a BER of 5.6 × 10-12 to serve multichannel application in next generation passive optical network.

A Self-feedback Colorless Fabry-Perot Laser Diode for 5 Gbit/s DWDM-PON

A remote-control-free self-feedback colorless FPLD transmitter with fiber Bragg grating based single-mode reflector is demonstrated for up to 5 Gbit/s DWDM-PON transmissions after 25 km with the aid of additional data-erased fiber loop.