Qing-Yang Xu

Characteristics of multimode fiber Bragg gratings and their influences on external-cavity semiconductor lasers

Characteristics of multimode fiber Bragg gratings (MMFBGs) are systematically studied. Dependence of the reflection spectra of MMFBG on excitation conditions, refractive-index change profile, and grating length is investigated experimentally. It is observed that the transmission spectra of the MMFBGs are more sensitive to the polarization state of input light than that of single-mode FBGs (SMFBGs). The influences of the fabrication conditions of MMFBGs (i.e., UV-exposure time) and the rotation of MMF on the output spectra of the MMFBG-based external-cavity semiconductor lasers are then investigated. It is found that the side-mode-suppression ratio and the spatial wavelength-locking region at a specific Bragg wavelength of an MMFBG are dependent on the refractive-index change profile of the grating.

Field-Sequential Operation of Laser Diode Pumped Nd : YVO

A compact modulated laser-diode pumped microchip green laser is presented based on optical-contact Nd : YVO4/periodically poled MgO : LiNbO3 (Nd : YVO4/PPMgLN) crystal. Linearly polarized green light of 450 mW was achieved with a maximum electrical-to-optical efficiency (EOE) of 16.25%. A peak power of 541.5 mW and an EOE of 13.9% was obtained when pumped by a peak current of 1.96 A. This green laser is designed for mobile laser display devices and has potential to be manufactured in mass production at low cost.

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— In this paper, a compact efficient diode-pumped solid-state (DPSS) green laser based on a periodically poled MgO:LiNbO3 (MgO:PPLN) crystal, which is suitable for low-cost mass production, was demonstrated. A linearly polarized 532-nm laser light of 1.02-W CW output power was obtained by employing a simple parallel-plane configuration. A numerical method, based on the 1 -D coupled-mode equations, is used in the cavity design and investigation of the intra-cavity second-harmonic-generation process.

/PPMgLN Microchip Green Laser

General time-domain traveling wave rate equations are employed for the simulation of the intra-cavity second harmonic generation (IC-SHG) of semiconductor lasers by a periodically poled nonlinear crystal waveguide. A 1060 nm high power, single-mode, ridge waveguide semiconductor laser is used in the simulation. The SHG crystal is a MgO-doped periodically poled lithium niobate with a single-mode ridge waveguide. Comparisons are made between the computed and experimental results of single-pass SHG for the purposes of model validation. The design of an IC-SHG green laser is further compared to the single-pass SHG laser in terms of the SHG output power, conversion efficiency, temperature tolerance, and high speed modulation capability. It is theoretically found that by using the IC-SHG configuration, SHG power and efficiency can be improved with a relatively short nonlinear crystal.

Watt‐level compact green laser for projection display

A novel watt-level compact green laser module (namely, mGreen), based on integrated Nd:YVO4 and MgO:PPLN crystals, is demonstrated for the first time. A linearly polarized 532-nm laser light of 1.28 W is obtained with an optical-to-optical conversion efficiency of 29.1%. The mGreen module is designed for green lasers with high power and low cost, which are in high demand in the laser display industry.

Theoretical Analysis of Intra-Cavity Second-Harmonic Generation of Semiconductor Lasers by a Periodically Poled Nonlinear Crystal Waveguide

An in-line diplexer optical transceiver chip based on an integrated DFB laser and photodiode has been demonstrated and analyzed. The transceiver transmits at 1310nm for upstream signal and receives at 1490nm for downstream signal. For the in-line integrated device, crosstalk between the transmitting and receiving channels become a key issue of system performance. Such crosstalk includes optical-optical, electrical-electrical, and electrical-optical crosstalk. The optical-optical crosstalk is caused by the limited optical isolation between the DFB laser and the photodiode. The electrical-electrical crosstalk is the result of electrical interference between transmitter driver and receiver amplifier. In the in-line transceiver design, the 1490nm downstream signal goes through the DFB laser cavity. When the laser is modulated, the 1490nm signal will experience modulation through the gain and refractive index change in the cavity. This electrical-optical crosstalk has been confirmed by numerical simulation and experimental measurement. The results show that the electrical-optical crosstalk power is proportional to the received 1490nm power and dependent on modulation depth of the DFB laser. A bit error rate model is also presented to describe the impact of the modulation crosstalk from the system performance point of view.

Compact Integrated Green Laser Module for Watt-Level Display Applications

In this paper, modulation crosstalk from 1310nm Distributed Feedback laser (DFB) upstream signals to 1490nm downstream signals in the monolithic integrated DFB-PD (Distributed Feedback laser-Photodiode) optical transceiver structure was simulated by the time-domain traveling wave (TDTW) rate equations numerically. It was found that high differential gain coefficient at 1490nm can contribute to the modulation crosstalk at about -25 to -30 dB. It was also found that the modulation crosstalk is modulation frequency dependent which will be enhanced about 3 dB at the relaxation oscillation frequency compared with low modulation frequency. Increasing modulation extinction ratio of the 1310nm DFB section from 10 to 18 dB, the crosstalk increases 3 dB. Such a higher modulation crosstalk (larger than -30 dB) should be considered since such crosstalk will degrade strongly the sensitivity of the 1490nm photo-detector.

Crosstalk analysis in in-line transceiver

A new compact green laser is demonstrated by using a mGreen module based on compact packaged MgO doped periodically poled lithium niobate (MgO:PPLN). The green laser can generate over 700-mW green light with an opticalto- optical efficiency of 29.6% and a volume of less than 7 cm3. The excellent performances of the MgO:PPLN based lasers, including high efficiency, compact size, low cost and being suitable to mass production, are very attractive for laser display applications.

Simulation of crosstalk in integrated distributed feedback laser-photodiode optical transceivers

In this paper, we report a novel LiNbO3 ridge waveguide fabrication technique based on the combination of Annealed Proton-Exchanging (APE) and precise diamond blade dicing. The process is ultra compact and compatible with periodically polled LiNbO3 (PPLN). By selecting optimized fabrication conditions, ridge waveguide with low propagation loss and single transmission mode can be formed at 1064nm and 1500nm wavelength, respectively. Such APE ridge waveguides have potential applications in optical communication, biomedical detection, and especially in nonlinear wavelength conversion.

MgO:PPLN based green lasers for portable laser projectors

In this paper, characteristics of the intra-cavity frequency doubled Nd:YYO4/PPMgO:LN green laser have been studied experimentally and theoretically. Two types of green laser strucutures, namely optical contact structure and separated structure, have been packaged for low power (100 mW) and high power (~1 W) applications, respectively. Coupled mode equations are used to investigate the green laser. The effect of the thermal dephasing along the propagation direction in the PPMgO:LN due to the heat generation by the linear absorption of the fundamental wave and linear and nonlinear absorption of the second hamonic (SH) wave is analyzed theoretically. By introducing the longitudinal temperature chirp in the PPMgO:LN crystal, the temperature tuning curve is enlarged by using a uniform PPMgO:LN grating.