A distributed feedback (DFB) laser for high-speed modulation with asymmetric corrugation-pitch-modulated (ACPM) grating structure and high-reflection and anti-reflection coating (HR-AR) coating is demonstrated theoretically and experimentally in this paper. The ACPM gating structure is fabricated by the reconstruction equivalent chirp (REC) technology, which is with low cost. The impact of the longitudinal spatial hole burning (LSHB) effect and the facet phase on the characteristics of the ACPM DFB laser is discussed in detail. The numerical simulation results show that the proposed ACPM DFB laser can suppress the LSHB effect significantly. Comparing with the conventional HR-AR DFB laser, the ACPM DFB laser can achieve higher output efficiency, better single-mode yield, and wider modulation bandwidth. The modulation eye diagrams of HR-AR DFB lasers with different grating structures are also presented. The experimental results show that the LSHB effect in the HR-AR DFB laser with ACPM structure is suppressed effectively. The laser with ACPM structure fabricated by the REC technique has high slope efficiency, stable single longitudinal mode operation, and wide modulation bandwidth.

We propose and theoretically analyze a hybrid transverse mode resonance DFB semiconductor laser which consists of one active section with π -phase shifted anti-symmetric Bragg grating ( π -ASBG) and two passive sections with uniform Bragg grating. The hybrid light resonance along with mode conversion between the fundamental transverse electric (TE ₀ ) mode and first order transverse electric (TE ₁ ) mode is formed by the π-ASBG. The emitted light from one facet with the TE ₀ or TE ₁ mode can be controlled by tuning the injection currents of the passive sections. As an example, a laser with ridge waveguide is designed and simulated. The transverse mode with the same wavelength is tuned by changing the injection currents of the passive sections. The suppression ratio between the two transverse modes reaches 18.4 dB and 18.7 dB when the TE ₀ and TE ₁ modes are emitted, respectively. A simple method for equivalently realizing the grating in the proposed laser was also analyzed. Therefore, as the transverse mode tunable light source, the proposed laser may benefit the future mode division multiplexing (MDM) systems for reconfigurability and more flexibility.

Single sideband (SSB) modulation based on a monolithic integrated optically injection-locked (MOIL) DFB laser is demonstrated experimentally. To our knowledge, this is the first time to realize SSB modulation utilizing a MOIL DFB laser. Tunable SSB signals with large lower-to-upper sideband power ratios are achieved by changing the bias currents of the MOIL DFB laser. The largest lower-to-upper sideband power ratio is measured to be 24.4 dB which is very useful for improving the transmission performance of a radio-over-fiber link. Due to the generated SSB modulation, the fiber transmission response is flattened significantly and a signal of 25 GHz is transmitted through 85-km fiber without being affected by the fiber chromatic dispersion. 20 MSymbol/s 32-QAM signals with subcarriers of 21 GHz, 23 GHz and 25 GHz are also transmitted by the proposed SSB modulation link, and both the error vector magnitude (EVM) and the error bit rate (EBR) of the link are improved distinctly. The proposed method can effectively suppress the effect of fiber chromatic dispersion.

The ongoing growth of data traffic from existing and new latency-sensitive applications poses a challenge to the data center network. Wavelength-routed optical circuit switching promises high bandwidth, low power and latency networking for data centers, but requires a wideband wavelength tunable source capable of nanosecond-scale hitless wavelength switching at every node. A tunable source based on DFB laser arrays is a potential candidate due to the high-speed dynamic property and high single-longitudinal-mode (SLM) stability of the DFB laser. However, the large-scale integration of the DFB laser and the high precision control of the lasing wavelength are still problems. In this work, we proposed and fabricated a monolithic integrated 16-channel DFB laser array with high SLM stability and 100-GHz channel spacing by using the reconstruction-equivalent-chirp (REC) technique. The maximum output power of each channel was above 6 mW. Based on the custom-designed fast switching drive board with a field-programmable gate array (FPGA), the switch-ON and OFF time between any pair of channel combinations were measured at less than 10 ns. Dynamic switching wavelengths remained stable and resided within the receiver bandwidth. Wavelength switching experiments for modulated light signals were done by driving the external modulator, achieving bit error performance at 1×10 ^-9 for 10 Gb/s NRZ data.

A large-capacity ultra-weak fiber Bragg grating (UW-FBG) array interrogation system is proposed and implemented. The system utilizes time- and wavelength-division multiplexing methods, based on a large-range tunable laser source (TLS) with fast tuning capability. The TLS consists of a distributed feedback multi-wavelength laser array (DFB-MLA) with a wavelength tuning range of 40 nm, which is realized using the reconstruction-equivalent-chirp (REC) technique. An external SOA modulator is used to modulate the output light from the TLS into nanosecond pulsed light. We establish an experimental system and successfully achieve 50 UW-FBGs interrogation. We perform temperature, strain, and vibration sensing experiments with a interrogation linearity of above 0.9995 and an error of less than 4 pm. Theoretically, the system is estimated to have an interrogation capability of more than 10,000 UW-FBGs, and the minimum spacing of adjacent UW-FBGs is 0.4 m. This research has made significant advancements in the multiplexing capability and spatial resolution of the UW-FBG array interrogation technology, offering important application potential in fields such as battery pack, structural health monitoring, and aerospace.

Optical switching based on arrayed waveguide grating routers (AWGRs) and fast tunable sources is a future-proof solution to overcome the bottleneck of limited bandwidth and high latency of electrical switches-based data center networks (DCNs). To support fine-grained optical packet switching and maintain high network throughputs, tunable sources capable of nanosecond-scale hitless wavelength switching are critical requirements for such fast optically switching networks. In this work, we experimentally demonstrate a fast-tunable source based on a high-density multi-wavelength DFB laser array monolithically integrated with a three-stage Y-branch combiner and an SOA. The DFB laser array has an average 100-GHz channel spacing under the same bias current. The output power of all lasers is above 10 mW, with a uniformity of less than 1 dB. Benefitting from the high-speed dynamic property of the DFB laser and high-speed burst drive pulses controlled by a field-programmable gate array (FPGA), less than 3 ns switching time is achieved by the on-off switching of the DFB laser on arrays, which is independent of tuning range. Furthermore, a 2 × 2 optical switching prototype based on this demonstrated chip and AWGRs achieves error-free transmission atop 25 Gbps NRZ per link with 12.8 ns end-to-end reconfiguration, which provides a path toward a high-bandwidth, low-latency, and energy-efficient wavelength-switched network for data centers in the post-Moore's Law era.