InP-Based Quantum Dot Lasers

Multi-wavelength distributed feedback laser array (DFB-MLA) based tunable semiconductor lasers have been widely used owing to the high mode stability and simple wavelength tuning scheme. In this paper, we proposed and experimentally demonstrated a matrix-grating tunable DFB laser array. And the reconstruction-equivalent-chirp (REC) technique is utilized to simplify grating fabrication and realize precise control of the grating phase. Traditionally, the laser is tuned by thermal-electric cooler (TEC), with large power consumption, slow wavelength tuning capability, and added device. To improve the wavelength tuning speed of laser, we varied laser's injection current instead of adjusting TEC's temperature. In addition, we analyzed the thermal influence of submount on the laser and then chose the SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> as the submount material for its low thermal conductivity and poor heat dissipation, resulting in wide wavelength tuning range via injection current. The DFB-MLA chip achieves a better tunable effect as the lasers can be tuned at 3.5-3.7 nm per channel from 50 to 120 mA with stable output power of over 3 mw as contrasted with the laser on the AlN submount being tuned at 1.4-1.5 nm per channel. And the chip has a side-mode suppressing ratio (SMSR) of over 35 dB and strong stability of wavelength in the repeated experiments. The proposed method may give a new way to realize the wide tuning range tunable DFB laser with a simple wavelength tuning mechanism in the future, especially for the applications of uncooled low-cost tunable lasers.

The application technology, in which coherent light was used, has been studied vigorously as the next generation optical communication and optical measurement systems. The LD source having the linewidth below 100 kHz and the tuning range over 10 nm is necessary for the coherent optical communication. The coherent light source having the more narrow linewidth and the more wide continuous tuning range is necessary for the optical measurement systems than the coherent optical communication. It is insufficient with present LD source in the performance target. The narrow linewidth and the wide continuous tuning range should be realized at the same time. Therefore, the design for the external cavity LD source is adopted in a ROR (Resonant Optical Reflector) structure and a sine-bar mechanism. The phase adjustment condition by the cavity length and the angle adjustment of the grating must be performed at the same time in the continuous tuning. Therefore, the sine-bar mechanism is used. The sine-bar mechanism adjusts automatically the angle of the grating, when adjusting the cavity length. The LD source is excellent in continuous tuning condition, when an equation presented is satisfied by the sine-bar mechanism. It could be continuously tuned in the wavelength range of 1511.2 nm - 1482.8 nm by the sine-bar mechanism. The minimum linewidth of 2.3 kHz was obtained by the ROR structure. A more wide continuous tuning range can be expected by improving the wavelength dispersion of the optical parts and the mechanics. >

Quasi phase-matching (QPM) is an attractive technique for optical wavelength conversion applications instead of the conventional birefringent phase matching. An advantage of the QPM is that any interaction within the transparency range of the material can be noncritically phase matched at a specific temperature by using the largest nonlinear optical coefficient. The periodically poled lithium niobate (PPLN) has been extensively used for the quasi phase-matched optical parametric oscillator (QPM-OPO). The effective nonlinear coefficient of the PPLN is 21.6 pm/V and enables one to realize efficient wavelength conversion. Usually the wavelength tuning of the QPM-OPO is achieved by changing the crystal temperature. Although the wide wavelength tuning range is achieved with the temperature tuning, the response is not fast. In this paper we demonstrate the wavelength tuning of the QPM-OPO by the electro-optic effect for fast wavelength tuning.

We present a wavelength-tunable laser diode with a 99-nm-wide wavelength tuning range. It has a compact wavelength-tunable filter with high wavelength selectivity fabricated using silicon photonics technology. The silicon photonic wavelength-tunable filter with wide wavelength tuning range was realized using two ring resonators and an asymmetric Mach-Zehnder interferometer. The wavelength-tunable laser diode fabricated by butt-joining a silicon photonic filter and semiconductor optical amplifier shows stable single-mode operation over a wide wavelength range.

We present a uniquely versatile and efficient mirror system capable of real-time fine-tuning in reflection and transmission properties across a broad wavelength range and at a high optical power. Leveraging the principles of the non-cyclic geometric phase (GP) acquired by the clockwise and counterclockwise beams of the Sagnac interferometer satisfying the anti-resonant condition on propagation through the quarter-wave plate, half-wave plate, and quarter-wave plate combination having fast axes oriented at 45° (fixed), θ (variable), and −45° (fixed) with respect to the vertical, respectively, our mirror system offers dynamic transmission control across 0–100% without the need for realignment. Notably, the GP-based mirror (GP-mirror) preserves the polarization state of the reflected beam, making it ideal for polarization-sensitive applications. The wavelength insensitivity of the GP enables seamless operation of the mirror across a wide wavelength range. As a proof-of-principle, we use the GP-mirror as the output coupler of a continuous-wave, green-pumped, doubly resonant optical parametric oscillator (DRO) based on a 30-mm-long MgO:sPPLT crystal and obtain stable operation at high powers over a wide wavelength tuning range. For a pump power of 5 W, the DRO provides an output power of 2.45 W at an extraction efficiency as high as 49% when operated at optimum output coupling. The DRO shows a maximum pump depletion of 89% and delivers an optimum output power across a tuning range ≥90 nm. The demonstrated concept offers a promising approach for advancing the capabilities and control of coherent optical sources tunable across different spectral regions and in all time scales from continuous-wave to ultrafast femtosecond domain.

We present a theoretical analysis of a newly demonstrated semiconductor laser with coupled distributed feedback and Fabry–Perot (DFB-FP) cavities and show that three modes of operation are possible for such a laser. In mode-switched DFB mode, the wavelength can be switched between longitudinal modes on either side of the stopband. In coupled-cavity laser mode, there are successive mode hops inside the stopband. Finally, in continuously tunable distributed Bragg reflector mode, a wide wavelength tuning range (4.8 Å) without mode hopping can be obtained. The analysis is general enough to be applied to any laser with a periodic waveguide section, and provides an understanding of the mechanisms and the limits of wavelength tuning in such lasers. This type of laser has very important applications in coherent optical communications.

In this work, we investigate an alternative directly modulated laser solution with applications to multiwavelength 25 Gb/s systems. The presented solution is based on a hybrid square/rhombus-rectangular laser (HSRRL), which consists of a Fabry–Pérot (FP) cavity and a square/rhombus microcavity (SRM). This structure is implemented and demonstrates single-mode lasing over a wide wavelength tuning range (30.8 nm). Single-mode operation is achieved with a side-mode suppression ratio (SMSR) greater than 30 dB and a linewidth of 10 MHz. Furthermore, with an electrical 3 dB bandwidth of 10 GHz. It is possible to directly modulate at 25 Gb/s with promising performance. These devices are simple and they are expected to meet the cost and power requirements of current networks.

Highly-integrated high-reliability widely-tunable femtosecond laser sources have important application values in various research and application fields, such as ultrafast spectroscopy, quantum optics, remote sensing and bio-imaging. In multi-photon excited fluorescence microscopy, femtosecond laser sources with moderate pulse energy and wide wavelength tunable range can not only meet the application requirements of the different tissue structures for the peak power and excitation wavelength, but also improve the nonlinear fluorescence efficiency and imaging resolution of the sample, and thus enhancing the penetration depth. Considering the extensive application prospect and important scientific research significance of the widely tunable femtosecond laser, in this paper we conduct an experimental research of the high repetition rate multi-wavelength femtosecond laser generation in compact sized and low-cost configuration based on the nonlinear propagation scheme of the high peak power femtosecond laser pulses in single-mode fiber. In experiment, we first construct a highly-integrated reliable all-polarization-maintaining fiber femtosecond laser amplifier, which mainly consists of an environmentally stable all-polarization-maintaining fiber mode-locked laser oscillator, single-mode fiber stretcher, a single-mode power pre-amplifier, a dual-cladding Yb-fiber amplifier, and transmission grating-pair compressor. Self-starting mode-locked operation is assured with a semiconductor saturable absorber mirror, and intra-cavity dispersion compensation is realized by a chirped fiber Bragg grating in the mode-locked oscillator. The mode-locked oscillator, which delivers laser pulses with center wavelength peaked at 1035 nm, is robust operation as temperature changes from 10℃ to 40℃ and the measured power fluctuation is less than 1% RMS over 168 hours at 23℃. The amplified high repetition rate laser pulses are compressed in a double-pass 1000 lines/mm transmission grating-pair compressor. After compression, laser pulses with 5.83 W average power and 264 fs pulse duration at 34 MHz repetition rate can be obtained. Simultaneously, we also study the dependence of the compressed pulse duration on the amplified output power. Employing a home-made high reliable compact sized all-polarization-maintaining fiber femtosecond laser as a pump source and low-cost single-mode fiber as a nonlinear medium, the generation technology of the widely tunable femtosecond laser in only fiber format is also studied based on the self-phase modulation nonlinear spectral broadening mechanism. Simultaneously, in order to reduce the effect of the dispersion on the spectral broadening as much as possible, an 80-mm-long fiber is used in experiment. The used single-mode spectral broadening fiber has a 6-m-diameter core and 20 fs2/mm dispersion coefficient. By coupling the femtosecond pump laser pulses into the 6-m-diameter fiber core, the output spectrum presents a significant nonlinear broadening. The coupled pump power can be continuously adjusted by a combination of a half-wave plate and a Glan laser polarizer. After bandpass filtering the leftmost and rightmost spectral lobes in self-phase modulation and self-steeping induced broadened spectrum with bandpass filters centered at 980, 1000, 1050, 1070 and 1100 nm, the laser pulses with 203, 195, 196, 187, and 194 fs pulse duration can be obtained at the corresponding center wavelengths. The experimental scheme presented in this paper, which is based on the nonlinear spectral broadening of the highreliability femtosecond laser pulse in single-mode fiber and the spectral selectivity technology, provides a new research approach to the realization of the highly-compacted reliable widely-tunable femtosecond laser sources and has important research significance.

Miniaturized tunable lasers are important as light sources in optical networks and sensing systems. However, challenges remain in realizing a low-cost on-chip tunable laser with high tuning accuracy and wide tuning range. Here, an external-cavity tunable laser integrated by using a pair of coupled-ring resonators as a reflector onto a single silicon chip is designed and demonstrated. The silicon coupled-ring reflector provides simultaneous tuning of the central reflective wavelength and the free spectral range of the entire cavity to guarantee phase matching. The effective optical length of the coupled-ring reflector is controlled by the complementary thermo-optic and free-carrier dispersion effects, thus enabling high-resolution wavelength fine-tuning while maintaining wide wavelength tuning range. Experimentally, the tunable laser has high external-cavity efficiency (22%) and high wavelength tuning accuracy (2 pm) throughout the 41.6 nm tuning range. Potential applications of the external-cavity tunable laser include optical networks, optical sensing, and on-chip optoelectronic systems.

We investigate self-seeded optical sources for interferometric sensing applications and show that they can, depending on optical filter bandwidth, provide high-output power, high wavelength temperature stability (<5 ppm/°C), low relative intensity noise (<-140 dBc/Hz) and low coherence lengths (<100 um). We characterize the key performance indicators for a range of optical filter bandwidths and provide insight into key design parameters of such sources for interferometric sensors.

Synergy of lead vacancies and morphotropic phase boundary to promote high piezoelectricity and temperature stability of PBZTN ceramics

New evaluating method and case study of thermal stability for asphalt pavement functional paving materials

Interference filter-stabilized external cavity diode lasers (ECDLs) have properties of simple configurations, high stabilities, and narrow linewidths. However, the interference filter used in common ECDL designs requires an ultra-narrow bandwidth (about 0.3 nm) to achieve mode selection, that is considerably expensive and not yet available for a wide range of wavelengths. In this paper, a robust ECDL using an available broad bandwidth (about 4 nm) interference filter as the wavelength discriminator is constructed and tested. The ECDL demonstrated a narrow Lorentzian fitted linewidth of 95 kHz and a spectral purity of 2.9 MHz. The long-term frequency stability of the ECDL reaches 5.59×10−12.

A study was made of the lasing characteristics of two new dyes belonging to the naphthalimide and benzanthrone classes, when they were pumped with the second harmonic of ruby laser radiation. The emission wavelength could be tuned over a range of ∼100 nm (from 500 to 600 nm in the case of naphthalimide and from 640 to 740 nm in the case of benzanthrone). The use of these compounds in lasers increased the output energy compared with the widely used coumarin 7 and uranin dyes in the green region or cresyl violet in the red region. Moreover, the new dyes ensured a considerably wider wavelength-tuning range.

An ultrastable heterostructured oxide catalyst based on high-entropy materials: A new strategy toward catalyst stabilization via synergistic interfacial interaction