Lingjuan Zhao

A frequency stabilization scheme for a wideband-tunable optoelectronic oscillator (OEO) based on fundamental and subharmonic RF injection locking is proposed, achieving a tuning range of 2–22 GHz with low phase noise. The injection-locked performance of the OEO using the fundamental RF signal and its 1/n subharmonic is investigated. The fundamental injection locking achieves a phase noise of <−130 dBc/Hz @ 10 kHz offset across the entire tuning range. An examination of phase noise behavior at different subharmonic orders reveals that fundamental and subharmonic injection locking achieve a five-order-of-magnitude improvement in Allan variance (0.1 s) and approximately 40 dB phase noise reduction at a 10 Hz offset from the carrier. This approach leverages the low-phase-noise advantage of the OEO while benefiting from the high stability of low-frequency external RF sources, enabling multi-frequency point frequency stabilization optimization.

We report the fabrication of a first electro-absorption modulated widely tunable DBR lasers (TEML) based on InGaAlAs multi-quantum well (MQW) material, which is superior than InGaAsP MQWs for the fabrication of both modulators and lasers. The device is fabricated by using butt-joint material growth technology and operates at a wavelength of 1.5 μm. An over 12 nm wavelength tuning range can be obtained. The characteristic temperature of the device is 83 K, which is notably higher than that for a laser based on InGaAsP MQWs. At 25 ℃, the electro-absorption modulator (EAM) of the device has a small signal modulation bandwidth exceeding 27 GHz, which is notably higher than the bandwidth for a TEML device having the same structure but InGaAsP MQW active material. At 25 Gb/s NRZ data modulation, to achieve 10E-10 bit error rate (BER), the power penalty after 5 and 10 km fiber transmission are 1 and 3 dB, respectively. The device is a promising low-cost light source for future high-capacity wavelength division multiplexing (WDM) optical communication systems.

We propose and study numerically a new deep ridge InGaAlAs/InP multi-quantum well (MQW) transistor lasers (TL), in which an n-doped InAlAs layer is inserted below the MQW layer in the device. High current gain can be obtained at the same time of laser operation, in contrast to the notable gain decreasing after lasing threshold in previous TLs. Because of the n-InAlAs layer, a normal graded index separate confinement heterostructure (GRIN-SCH) which helps to enhance the device modulation performance can be adopted. Thus, high quality electrical drivers can be expected to be integrated with high speed lasers with this InGaAlAs/InP TL structure.

A novel wavelength triplexer based on Channel-Shaped Multimode Interference (C-MMI) structures on the InP platform is proposed for multi-channel integration compatibility in a 50G passive optical network (PON) system. Performance analysis of the proposed device is carried out by using the 3D Beam Propagation Method (3D-BPM), which shows excellent properties with insertion loss < 0.5 dB and low crosstalk < −14 dB for the 1342 nm in the Original band (1260–1360 nm), 1490 nm in the Short wavelength band (1460–1530 nm), and 1577 nm in the Long wavelength band (1565–1625 nm), also known as the OSL wavelengths band. Furthermore, the passbands of the three downlink channels of 1342 nm, 1490 nm, and 1577 nm, reach 14 nm, 20 nm, and 64 nm, respectively, which is wide enough to meet the 50G PON optical line terminal (OLT) requirement. Additionally, the proposed device is extremely compact with a total length of only 448 μm, making it attractive in the monolithic integrated laser chip and OLT packaged module.

A differential multi-frequency laser Doppler velocimetry is demonstrated, utilizing the synchronized multimode of a mode-locked distributed Bragg reflector laser. This scheme enables the simultaneous detection of multiple Doppler frequency shifts. Multiple differential Doppler shifts of 0.6 Hz, 1.3 Hz, and 1.9 Hz are obtained, with an average speed of 3.677 mm/s and a standard deviation of 0.122 mm/s, demonstrating a cross-referenced velocity measurement capability. The measurement results are also compared with the dual-frequency laser Doppler velocimetry scheme using electro-optical modulation.

We demonstrated a repetition-rate-tunable self-mode-locked optically pumped semiconductor disk laser (OP-SDL). The highest repetition rate of mode-locked pulses was 6.13 GHz. When using an output mirror with a radius of curvature of 300 mm, the tuning range was from 0.6 GHz to 4.35 GHz. When replaced by an output mirror with a radius of curvature of 50 mm, the tuning range was from 3.13 GHz to 6.13 GHz. The entire tuning process was continuous, and OP-SDL was always in a stable mode-locked working state. To the best of our knowledge, this is the first work to obtain repetition rate of 6.13 GHz and tunable laser in self-mode-locked OP-SDLs. 3.75 GHz was the maximum tuning range of repetition rate at present.

We report a novel high speed directly modulated dual wavelength 1.3 μm laser for THz communication applications. The laser has a compact size and simple structure, which consists a DFB section and a passive distributed Bragg reflector (DBR) section, leading to a device fabrication procedure similar to that of a normal DFB laser. The laser has an over 26 GHz modulation bandwidth in the dual wavelength working mode, which facilitates high speed data modulation onto THz wave. NRZ data modulations at up to 50 Gb/s have been demonstrated successfully. The bit error rate (BER) performances under 10 and 25 Gb/s NRZ data modulation are studied. 10 ^-10 BER can be obtained and the 10 km fiber transmission power penalty when compared with the back to back transmissions is less than 0.5 dB. This device is a low-cost but powerful light source for future photonics based high speed THz communication system.

We have fabricated $1.3~\mu \text{m}$ band InP based high speed directly modulated distributed feedback (DFB) lasers having passive distributed Bragg reflector (DBR). Because of the feed back from the DBR section, the modulation bandwidth of the lasers is over 25 GHz, which is notably larger than the 19 GHz for a normal single section DFB laser. The reflector of the devices has the same multi-quantum wells (MQWs) as the DFB section, which simplifies the device fabrication greatly, helping to lower the device cost. For the DBR integrated DFB lasers, experimental results show that a larger modulation current efficiency can be obtained when the DFB wavelength is more positively detuned relative to the reflection peak of the DBR reflector. This indicates that a static detune between the DFB wavelength and the DBR reflection peak can be introduced into a distributed reflector laser to get a good detune condition, helping to lower the device cost of high speed directly modulated lasers.

The optical feedback tolerance (OFT) of a distributed Bragg reflector (DBR) laser was investigated experimentally. The static and modulation performance of the DBR laser under optical feedback was examined by evaluating its relative intensity noise (RIN) and bit error rate (BER). It is shown that the OFT of the DBR laser is closely related to its peak wavelength detuning relative to the Bragg wavelength. A high tolerance to optical feedback was demonstrated, both in the continuous wave (CW) and the direct modulation (DM) states, when the DBR laser was red-detuned relative to the Bragg wavelength. The excess RIN induced by optical feedback was well suppressed to a level of −140 dB/Hz at a feedback level of −9 dB in the CW state. In a 10 Gbps direct modulation state, bit error rates (BER) below 1 × 10⁻⁹ and 3 × 10⁻⁷ were obtained under a feedback level of −15 dB and −9 dB, respectively, for the case of back-to-back transmission. After 20 km fiber transmission, the BER still maintained below 1 × 10⁻⁷ under a feedback level of −15 dB, with a power penalty of less than 1 dB.