Hsiang-Yu Chen

450-nm GaN laser diode enables high-speed visible light communication with 9-Gbps QAM-OFDM

A TO-38-can packaged Gallium nitride (GaN) blue laser diode (LD) based free-space visible light communication (VLC) with 64-quadrature amplitude modulation (QAM) and 32-subcarrier orthogonal frequency division multiplexing (OFDM) transmission at 9 Gbps is preliminarily demonstrated over a 5-m free-space link. The 3-dB analog modulation bandwidth of the TO-38-can packaged GaN blue LD biased at 65 mA and controlled at 25°C is only 900 MHz, which can be extended to 1.5 GHz for OFDM encoding after throughput intensity optimization. When delivering the 4-Gbps 16-QAM OFDM data within 1-GHz bandwidth, the error vector magnitude (EVM), signal-to-noise ratio (SNR) and bit-error-rate (BER) of the received data are observed as 8.4%, 22.4 dB and 3.5 × 10(-8), respectively. By increasing the encoded bandwidth to 1.5 GHz, the TO-38-can packaged GaN blue LD enlarges its transmission capacity to 6 Gbps but degrades its transmitted BER to 1.7 × 10(-3). The same transmission capacity of 6 Gbps can also be achieved with a BER of 1 × 10(-6) by encoding 64-QAM OFDM data within 1-GHz bandwidth. Using the 1.5-GHz full bandwidth of the TO-38-can packaged GaN blue LD provides the 64-QAM OFDM transmission up to 9 Gbps, which successfully delivers data with an EVM of 5.1%, an SNR of 22 dB and a BER of 3.6 × 10(-3) passed the forward error correction (FEC) criterion.

Phosphorous Diffuser Diverged Blue Laser Diode for Indoor Lighting and Communication.

An advanced light-fidelity (Li-Fi) system based on the blue Gallium nitride (GaN) laser diode (LD) with a compact white-light phosphorous diffuser is demonstrated for fusing the indoor white-lighting and visible light communication (VLC). The phosphorous diffuser adhered blue GaN LD broadens luminescent spectrum and diverges beam spot to provide ample functionality including the completeness of Li-Fi feature and the quality of white-lighting. The phosphorous diffuser diverged white-light spot covers a radiant angle up to 120o with CIE coordinates of (0.34, 0.37). On the other hand, the degradation on throughput frequency response of the blue LD is mainly attributed to the self-feedback caused by the reflection from the phosphor-air interface. It represents the current state-of-the-art performance on carrying 5.2-Gbit/s orthogonal frequency-division multiplexed 16-quadrature-amplitude modulation (16-QAM OFDM) data with a bit error rate (BER) of 3.1 × 10−3 over a 60-cm free-space link. This work aims to explore the plausibility of the phosphorous diffuser diverged blue GaN LD for future hybrid white-lighting and VLC systems.

Remote heterodyne millimeter-wave over fiber based OFDM-PON with master-to-slave injected dual-mode colorless FPLD pair

A remote heterodyne millimeter-wave (MMW) carrier at 47.7 GHz over fiber synthesized with the master-to-slave injected dual-mode colorless FPLD pair is proposed, which enables the future connection between the wired fiber-optic 64-QAM OFDM-PON at 24 Gb/s with the MMW 4-QAM OFDM wireless network at 2 Gb/s. Both the single- and dual-mode master-to-slave injection-locked colorless FPLD pairs are compared to optimize the proposed 64-QAM OFDM-PON. For the unamplified single-mode master, the slave colorless FPLD successfully performs the 64-QAM OFDM data at 24 Gb/s with EVM, SNR and BER of 8.5%, 21.5 dB and 2.9 × 10(-3), respectively. In contrast, the dual-mode master-to-slave injection-locked colorless FPLD pair with amplified and unfiltered master can transmit 64-QAM OFDM data at 18 Gb/s over 25-km SMF to provide EVM, SNR and BER of 8.2%, 21.8 dB and 2.2 × 10(-3), respectively. For the dual-mode master-to-slave injection-locked colorless FPLD pair, even though the modal dispersion occurred during 25-km SMF transmission makes it sacrifice the usable OFDM bandwidth by only 1 GHz, which guarantees the sufficient encoding bitrate for the optically generated MMW carrier to implement the fusion of MMW wireless LAN and DWDM-PON with cost-effective and compact architecture. As a result, the 47.7-GHz MMW carrier remotely beat from the dual-mode master-to-slave injection-locked colorless FPLD pair exhibits an extremely narrow bandwidth of only 0.48 MHz. After frequency down-conversion operation, the 47.7-GHz MMW carrier successfully delivers 4-QAM OFDM data up to 2 Gb/s with EVM, SNR and BER of 33.5%, 9.51 dB and 1.4 × 10(-3), respectively.

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.

Four-Wave-Mixing Suppression of Master-to-Slave Injection-Locked Two-Wavelength FPLD Pair for MMW-PON

The four-wave-mixing (FWM) suppression of a master-to-slave injection-locked two-wavelength Fabry-Perot laser diode (FPLD) pair is investigated from the viewpoint of integrating fiber-optic wired and millimeter-wave (MMW) wireless networks for mobile and satellite communications. This is achieved by shifting the FWM side modes away from the cavity mode to avoid FWM enhancement induced by cavity resonance. Mode-deviated two-wavelength injection from a 900-μm master FPLD to a 600-μm slave FPLD successfully suppresses the resonant FWM side modes to -31 and -35 dBm, which enables the transmission of 18-Gb/s 64-quadrature amplitude modulation orthogonal frequency-division multiplexing (QAM OFDM) data with error vector magnitude (EVM), signal-to-noise ratio (SNR), and bit error rate (BER) values of 6.3%, 24 dB, and 1.6 × 10-4, respectively. The FWM-suppressed 600-μm slave shows lower chromatic dispersion than that of the 750-μm slave. In addition, a 47-GHz MMW carrier remotely beat by the two-wavelength-injected slave enables the transmission of passband 2-Gb/s 4-QAM OFDM data with EVM, SNR, and BER values of 36.3%, 8.8 dB, and 2.9 × 10-3, respectively, after 25-km single-mode fiber wired and 1.6-m free-space wireless transmission.

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.

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.

Can silicon carbide serve as a saturable absorber for passive mode-locked fiber lasers?

The study presents a novel demonstration of a passively mode-locked erbium-doped fiber laser (EDFL) that is based on a silicon carbide (SixC1−x) saturable absorber. When the C/Si composition ratio is increased to 1.83, the SixC1−x film transforms from two-photon absorption to nonlinear saturable absorption, and the corresponding value reaches −3.9 × 10−6 cm/W. The Si-rich SixC1−x film cannot mode lock the EDFL because it induced high intracavity loss through two-photon absorption. Even when a stoichiometric SiC is used, the EDFL is mode locked, similar to an EDFL operating under weak nonlinear-polarization-rotation condition. A C-rich SixC1−x film containing sp2-orbital C–C bonds with a linear absorbance of 0.172 and nonlinear absorbance of 0.04 at a 181 MW/cm2 saturation intensity demonstrates nonlinear transmittance. The C-rich SixC1−x saturable absorber successfully generates a short mode-locked EDFL pulse of 470 fs. The fluctuation of the pulse-train envelope dropps considerably from 11.6% to 0.8% when a strong saturable-absorption-induced self-amplitude modulation process occurs in the C-rich SixC1−x film.

Millimeter-Wave Carrier Embedded Dual-Color Laser Diode for 5G MMW oF Link

With the use of central carrier suppressed master which contains a double sideband carrier, a directly encoded dual-color laser diode with low coherence based millimeter-wave (MMW) carrier generation for hybrid wired and wireless MMW over fiber (MMWoF) system is demonstrated. The maximal transmission capacities for optical wired band at 36 Gb/s and for MMW wireless band at 12 Gb/s are achieved in the proposed MMWoF link. Three MMW carrier frequencies of 28, 39, and 47 GHz are synthesized for implementing the fifth generation (5G) mobile network and satellite communication. The dual-color injection-locking effectively suppresses the central carrier power to –37 dBm, which provides the dual-color optical carrier with a central carrier suppression ratio of 38 dB. The 47-GHz double sideband carrier injection has shown its capability to carry 64-QAM OFDM data at 36 Gb/s with the lowest bit-error-rate (BER) of 2.1 × 10–3 over 25-km single-mode fiber, as its weakest four-wave-mixing modes greatly suppress the fiber chromatic dispersion. After optical baseband transmission, the photonic mixed 28-, 39-, and 47-GHz MMW carriers are heterodyne beat from the dual-color carrier to show similar spectral linewidth of <1.2 Hz and carrier-to-noise ratio of >41 dB. The 28-GHz MMW carrier can wireless transmit 12-Gb/s 16-QAM OFDM data over 1.6-m free-space to show an average signal-to-noise ratio of 15.3 dB, an error vector magnitude of 17.1%, and a receiving BER of 3.3 × 10-3.

Corrigendum: Can silicon carbide serve as a saturable absorber for passive mode-locked fiber lasers?

Scientific Reports 5: Article number: 16463; 10.1038/srep16463 published online: November122015; updated: March102016 The original version of this Article contained typographical errors in the spelling of the authors Chao-Kuei Lee and Chih-I Wu which were incorrectly given as Chao-Kuei Leeb and Chih-I Wua respectively. In addition, there were errors in the Acknowledgements section. “The authors thank the Ministry of Science and Technology, Taiwan, R.O.C., and the Excellent Research Projects of National Taiwan University, Taiwan, for financially supporting this research under grants NSC 101-2221-E-002-071-MY3, and MOST 103-2221-E002-042-MY3, 104-2221-E-002 -117 -MY3, 103R89081 and 103R89083.” now reads: “The authors thank the Ministry of Science and Technology, Taiwan, R.O.C., and Excellent Research Projects of the National Taiwan University, Taiwan, R.O.C., for financially supporting this research under grants MOST 103-2221-E002-042-MY3, MOST- 104-2221-E-002 -117 -MY3, NTU-ERP-105R89081 and NTU-ERP-105R89083.” These errors have now been corrected in the PDF and HTML versions of the Article.