Limeng Zhang

Widely Tunable Narrow-Linewidth Lasers Using Self-Injection DBR Lasers

A widely tunable distributed Bragg reflector (DBR) laser with kilohertz linewidth output is demonstrated using a dual-loop self-injection scheme. The self-injection-locked narrow linewidth DBR laser can be tuned by 13 nm, covering 18 channels, with side mode suppression ratios over 38 dB and linewidths all <;10 kHz.

Tunable optical microwave generation using self-injection locked monolithic dual-wavelength amplified feedback laser

A tunable optical microwave generation scheme using self-injection locked monolithic dual-wavelength amplified feedback laser (AFL) is proposed and experimentally demonstrated. By using a dual-loop feedback scheme, the 3-dB linewidth of the optical microwave output resulting from mode beating is reduced from MHz to kHz scale. Optical microwave generation tunable from 30 to 38 GHz with 3-dB linewidth below 2 kHz is experimentally demonstrated.

C-band fundamental/first-order mode converter based on multimode interference coupler on InP substrate*

The design, fabrication and characterization of a fundamental/first-order mode converter based on multimode interference coupler on InP substrate were reported. Detailed optimization of the device parameters were investigated using 3D beam propagation method. In the experiments, the fabricated mode converter realized mode conversion from the fundamental mode to the first-order mode in the wavelength range of 1530-1565 nm with excess loss less than 3 dB. Moreover, LP 01 and LP 11 fiber modes were successfully excited from a few-mode fiber by using the device. This InP-based mode converter can be a possible candidate for integrated transceivers for future mode-division multiplexing system.

Widely Tunable Amplified Feedback Laser With Beating-Frequency Covering 60-GHz Band

A monolithic integrated amplified feedback laser is experimentally demonstrated as a new solution to generate dual-mode lasing with a wide frequency tuning range covering the entire 60-GHz band. This laser consists of a complex-coupled distributed feedback laser and an integrated feedback cavity formed by a phase section and an amplifier section. Different laser sections are integrated by a simple quantum well intermixing technique. By tuning the injection currents of the laser sections, the beating-frequency can be continuously tuned from 46.8 to 72 GHz with a 3-dB linewidth below 5 MHz. Benefit from the simple fabrication process and wide tuning range, the device will be a potential candidate for hybrid fiber-wireless access network and high frequency optical microwave generation.

A Widely Tunable Directly Modulated DBR Laser With High Linearity

We demonstrate a widely tunable and high-modulation-bandwidth distributed Bragg reflector (DBR) laser. With the selected butt-joint material (λg = 1.44 μm) and butt-joint angle (45°) for the grating section, a widely tuning range of 13.88 nm with 19 consecutive channels is obtained for the two-section DBR laser. Furthermore, a small-signal modulation bandwidth of 16 GHz with in-band flatness of ±3 dB is realized at 10 °C. A uniform modulation bandwidth of more than 13 GHz is obtained for ten consecutive channels at 25 °C. Meanwhile, the DBR laser shows a high linearity, with an input 1-dB compression point of 17 dBm and an input third-order intercept point of 30 dBm at 13 GHz.

Disordered Tm:Ca 9 La(VO 4 ) 7 : a novel crystal with potential for broadband tunable lasing

We report on the crystal growth, structural and spectroscopic investigation of a novel trigonal calcium vanadate crystal, Tm3+:Ca9La(VO4)7. Polarized absorption, stimulated-emission and gain cross-section spectra are determined for this material. The maximum σSE corresponding to the 3F4 → 3H6 transition amounts to 1.28 × 10−20 cm2 at 1854 nm for σ-polarization. The measured lifetime of the Tm3+ ions in the 3F4 state is 1.19 ms. The Judd-Ofelt analysis performed yielded intensity parameters of Ω2 = 4.682, Ω4 = 0.659 and Ω6 = 0.475 [10−20 cm2]. The polarized Raman spectra indicate a strong and broad band centered at 867 cm−1. Owing to the disordered nature of Ca9La(VO4)7, the Tm3+ ions exhibit a broad and smooth gain profile at ~2 μm. The spectroscopic properties of Tm3+:Ca9La(VO4)7 are very promising for broadly tunable and ultrashort pulse lasers near 2 µm.

Long-range and high-resolution correlation optical time-domain reflectometry using a monolithic integrated broadband chaotic laser

We experimentally demonstrate a compact, long-range, high-resolution chaotic correlation optical time-domain reflectometry based on a monolithic integrated chaotic laser (MICL). The MICL can directly generate a broadband chaotic signal covering a RF frequency range of over 40 GHz. Multi-reflection events can be precisely located in a detection range of ∼47  km with a range-independent resolution of 2.6 mm.

Widely tunable monolithic dual-mode laser for W-band photonic millimeter-wave generation and all-optical clock recovery

We demonstrate a monolithic dual-mode amplified feedback laser for photonic millimeter-wave generation and all-optical clock recovery. Dual-mode lasing with beating frequency around 100 GHz was realized by using a single-mode distributed feedback (DFB) laser with a short feedback cavity that was integrated by simple quantum-well intermixing technology. By tuning the bias currents of the laser sections, the beating-frequency can be continuously tuned from 75 to 109 GHz, almost covering the entire W-band (75-110 GHz). Furthermore, by using this device, an all-optical clock recovery for 100 Gbit/s return-to-zero on-off-keying signal was achieved with a timing jitter of 301 fs.

640-Gbit/s fast physical random number generation using a broadband chaotic semiconductor laser

An ultra-fast physical random number generator is demonstrated utilizing a photonic integrated device based broadband chaotic source with a simple post data processing method. The compact chaotic source is implemented by using a monolithic integrated dual-mode amplified feedback laser (AFL) with self-injection, where a robust chaotic signal with RF frequency coverage of above 50 GHz and flatness of ±3.6 dB is generated. By using 4-least significant bits (LSBs) retaining from the 8-bit digitization of the chaotic waveform, random sequences with a bit-rate up to 640 Gbit/s (160 GS/s × 4 bits) are realized. The generated random bits have passed each of the fifteen NIST statistics tests (NIST SP800-22), indicating its randomness for practical applications.

A Widely Tunable Optoelectronic Oscillator Based on Directly Modulated Dual-Mode Laser

A widely tunable optoelectronic oscillator (OEO) based on a directly modulated monolithic integrated dual-mode amplified feedback laser (AFL) is proposed and experimentally demonstrated. In this OEO scheme, the functions of the laser source, the intensity modulator, and the tunable high-