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Flexible wavelength tunability is a critical specification for second‐harmonic generation (SHG) light sources. In the evolving landscape of future technologies, the photonic crystal (PhC) vertical cavity emerges as a promising platform for developing ultracompact SHG devices. However, the reduced size of PhC vertical cavities necessitates a departure from conventional tuning methodologies rooted in traditional phase‐matching frameworks. In this study, an SHG tuning strategy is presented that exploits the relationship between the resonance properties of the cavity and its SHG response. By systematically adjusting the incident angle of fundamental light, we demonstrate the precise tuning of cavity resonance, consequently tuning the SHG conversion efficiency spectra across a spectral bandwidth of about 30 nm. This research contributes to profound understanding of the physical process for flexible wavelength tunability at the nanoscale beyond conventional phase‐matching frameworks, offering insights for the development of tunable SHG sources in integrated photonics and nanoscale optical devices. [ABSTRACT FROM AUTHOR]

Single-photon emitters (SPEs) hold the key to many quantum technologies including quantum computing. In particular, developing a scalable array of identical SPEs can play an important role in preparing single photons – crucial resources for computation – at a high rate, allowing to improve the computational capacity. Recently, different types of SPEs have been found in various 2D materials. Towards realizing scalable SPE arrays in 2D materials for quantum computation, it is required to develop tunable SPEs that can produce identical photons by precisely controlling emission properties. Here, we present a brief review of the recent progress on various tuning methods in different 2D materials. Firstly, we discuss the operation principle of different 2D SPEs along with their unique characteristics. Secondly, we introduce various dynamic strain engineering methods for tuning the emission wavelengths in 2D SPEs. We also present several electric field-induced wavelength tuning methods for 2D SPEs. Lastly, we discuss the outlook of dynamically tunable 2D SPEs towards scalable 2D SPE arrays for realizing practical quantum photonics applications. [ABSTRACT FROM AUTHOR]

Birefringence, quantified as the maximum effective index difference of two orthogonally polarized modes, is one of the key characteristics of Lithium Niobate on Insulator (LNOI) waveguide devices. As LNOI optical properties strongly depend on the polarization of the propagating light beam, achieving the zero‐birefringence condition (ZBC) is highly desired. In this work, a rib LNOI waveguide is designed, and the influence of geometrical dimensions on the birefringence is characterized. From the result, the slab's height is found to be the dominant geometrical factor that significantly contributes to the birefringence, with an optimum slab's height found at 50 nm. For this optimized value, the influence of width and wavelength on birefringence are characterized. The analysis is extended to investigate the properties of group indices that can result in the temporal walk‐off phenomenon. This phenomenon can significantly impact the performance of single‐photon devices, as it can cause a polarization mismatch between the incident photon and the polarization properties of the medium, resulting in reduced efficiency of devices such as single‐photon detectors. In the analysis, the zero birefringence and walk‐off are achieved at narrow waveguide width, 푤 of 250 nm and wavelength, λ${\mathrm{\lambda }}$ = 1500 nm, which is within the telecommunication region band. [ABSTRACT FROM AUTHOR]

We describe an all-optical method to achieve—prior to further advanced processing steps—a perfect match of the relevant wavelength-sensitive parameters of an InGaN/GaN semiconductor distributed feedback laser. Instead of permanently etching and epitaxially over-growing a waveguide-based diffraction grating for the definition of an index-coupled distributed feedback laser, we suggest here—by employing a powerful ultraviolet pump laser—a non-permanent, photoinduced generation of an optical diffraction grating. The resulting complex refractive index modulation then forms a gain-coupled distributed feedback laser. Such an approach has the advantage of remaining flexible as long as possible—both in terms of the correct grating period and the ideal coupling constant. This flexibility is maintained until the definitive etch and the epitaxial over-growth of the diffraction grating are completed. Such devices can—like their dye laser counterparts in the early seventies—also be used as ultra-broadly tunable single-mode sources. [ABSTRACT FROM AUTHOR]

The field of optoelectronic integrated circuits is actively developing reliable and efficient room-temperature continuous-wave (CW) lasers. CW-pumped lasers combine the economical and simple manufacturing processes of colloidal semiconductor lasers with the efficient and stable output of continuous pumping, enabling them to significantly impact the field of semiconductor lasers. However, development is still severely challenged by limitations such as gain materials and cavity structures. Consequently, as a compromise, most colloidal semiconductor lasers proposed to date have relied on another pulsed laser as the pumping source. In this study, a self-assembled colloidal topological laser is proposed that benefits from CW pumping at room temperature. By utilizing an interfacial self-assembly strategy, nanoplatelets (NPLs) are managed to control the collective orientation (face-down or edge-up), achieving controlled polarization of amplified spontaneous emission for the first time. Furthermore, precise control over the thickness of a single NPL layer is demonstrated, which enables the laser system to offer extensive wavelength tunability (over 50 nm), ultra-high polarization (over 95%), and good temporal stability. These metrics signify the optimal performance level of colloidal semiconductor lasers, marking a new era in solution processing systems for the optoelectronic integrated circuit field., (© 2025 The Author(s). Advanced Materials published by Wiley‐VCH GmbH.)

We describe an all-optical method to achieve—prior to further advanced processing steps—a perfect match of the relevant wavelength-sensitive parameters of an InGaN/GaN semiconductor distributed feedback laser. Instead of permanently etching and epitaxially over-growing a waveguide-based diffraction grating for the definition of an index-coupled distributed feedback laser, we suggest here—by employing a powerful ultraviolet pump laser—a non-permanent, photoinduced generation of an optical diffraction grating. The resulting complex refractive index modulation then forms a gain-coupled distributed feedback laser. Such an approach has the advantage of remaining flexible as long as possible—both in terms of the correct grating period and the ideal coupling constant. This flexibility is maintained until the definitive etch and the epitaxial over-growth of the diffraction grating are completed. Such devices can—like their dye laser counterparts in the early seventies—also be used as ultra-broadly tunable single-mode sources.

The ICD phenomenon has drawn a lot of attention in recent years in applicable fields such as chiral sensing and chiroptical devices. In this work, we first gaze at the issues of thin spin‐coated films not being able to deliver consistent ICD signals. A hypothesis of the underlying problem is proposed through a brief elucidation of the spin‐coating process. To confirm and eliminate the uncontrollable dynamic factors with spin coating, we then dedicate our efforts to develop a new gel system based on chiral L‐/D‐N′,N′‐Dibenzoyl‐cystine. Achiral dye molecules are intercalated in a DBC gel through a "one‐step" preparation procedure. Compared to the former spin‐coating system, significantly improved reproducibility of the new gel system is demonstrated. Besides, the ICD signals can be customized in a broad spectral range (wavelength tunability) by substituting dye molecules. Finally, we discuss the potential applications of this interesting system. [ABSTRACT FROM AUTHOR]

The multi‐functional phototransistor is essential for the realization of highly‐integrated multi‐functional electronics. Herein, inverse photomemory is discovered from the organic phototransistor based on dinaphtho[2,3‐b:2′,3′‐f]thieno[3,2‐b]thiophene (DNTT)/diarylethene (DAE) bilayer structure. With the incorporation of the photoactive DAE dielectric layer, the integration of high‐performance photodetection and photomemory in one device is realized. The function of the device can be switched by changing the wavelength of the incident light. The devices exhibit positive photosensing performances under the stimulation of 450 nm monochromatic light, can be switched to inverse photomemory transistors under the stimulation of 365 nm monochromatic light, and recover to the pristine state when applying a positive gate voltage and 600 nm illumination. The I450/Idark ratio of positive photosensing and the Idark/I365 ratio of inverse photomemory are high up to the order of 106 and 107, respectively. In addition, the photonic logic gate and the retina emulation have been successfully demonstrated. In addition, the device can be operated as a light‐stimulated synaptic transistor. The typical synaptic behaviors (excitatory postsynaptic current, paired pulse facilitation, memory, and learning behaviors) have been successfully demonstrated. The development of multi‐functionalized phototransistors provides a promising configuration for multi‐functional and highly‐integrated systems. [ABSTRACT FROM AUTHOR]

A detailed experimental investigation of the effects of external optical injection on a Fabry Perot laser when in continuous wave (CW) mode and in gain switched mode is presented. Such detailed characterisation can help in optimising operating condition of the transmitters to significantly improve the system performance for dedicated applications. In CW mode, we characterised various performance indicators of a laser such as side mode suppression ratio (SMSR), wavelength, peak power, modulation bandwidth, resonance frequency, optical linewidth, and phase noise under external optical injection with the use of tuning maps. We also present in brief the theoretical origin of these parameters using rate equations. We then investigated the performance of the externally injected Fabry Perot laser under gain switching for optical frequency comb (OFC) generation. We demonstrated the generation of an OFC with a free spectral range of 6.25 GHz to 25 GHz and a quasi-continuous wavelength tunability of 31 nm. The phase noise of the tones of the generated OFC is measured and is found to be similar to that of the externally injected light and the measured optical linewidth was ∼40 kHz. We also presented experimentally the trade-off that exists between bandwidth of the generated OFC and the phase noise of individual comb tones under external optical injection and their optimisation for the application at hand. [ABSTRACT FROM AUTHOR]

A wavelength-tunable high repetition rate (HRR) erbium-doped fiber laser in L-band based on dissipative four-wave mixing (DFWM) mechanism is demonstrated. The cavity can generate a single-soliton train and bound-soliton train with a fixed repetition rate of ~126 GHz, which is determined by the free spectral range of the intra-cavity Lyot filter. A wide wavelength-tuning operation can also be obtained by rotating the polarization controllers. The wavelength-tuning ranges of the HRR single-soliton state and HRR bound-soliton state are ~38.3 nm and ~22.6 nm, respectively. This laser provides useful references for the area of a wavelength-tunable fiber laser with high repetition rate. The laser may also find useful applications in high-speed communication, sensing, etc.

A silicon-based laser is a critical component in the realization of full silicon (Si) photonic integrated circuits due to advantages in cost-competitive integration with the mature digital technology. The poor optical gain stemming from the indirect energy band structure of Si, however, has been a hurdle to realize this goal. An efficient Si nanocavity can become a key enabler to overcome the hurdle by earning the interaction time for ephemeral photons. Here, we propose a weakly tapered Si nanopillar whispering-gallery-mode resonator as a wavelength- scale Si cavity platform, which is suitable for lasing. We observe spatially well-separated and nondegenerate modes in the wide near-infrared spectral regime while maintaining a high quality factor. Mode analysis via experiments and simulations confirms spectrally and spatially well-separated resonant modes, suggesting that the diameter and slope of the Si nanopillar are crucial determinants for the formation and control of whispering gallery modes. Considering the versatile spectral tunability and selectivity with the high reproducibility, the proposed nanopillars can be a pathway that leads to compact Si-based lasers. [ABSTRACT FROM AUTHOR]

Adopting the pay-as-you-grow approach to upgrade passive optical network (PON) facilities by WDM technology insures the smoothness of the upgrade, and also results in the coexistence of wavelength-fixed/tunable optical network units (ONUs) in WDM/TDM PONs. Dynamic bandwidth allocation (DBA) is the key to support such coexistence of heterogeneous ONUs. Thus, DBA is also the key to support the smooth evolution of PONs. To more fairly coordinate the bandwidth allocation among the coexisting heterogeneous ONUs, a differentiated grant sizing (DGS) scheme is proposed. In DGS, not only the fairness between the wavelength-fixed/tunable ONUs but also the fairness between the lightly/heavily loaded ONUs is taken into account. To further carry out load balancing among wavelengths, a grant scheduling scheme is also proposed to cooperate with the grant sizing scheme. In the grant scheduling scheme, a measure of the ONUs’ flexibility is given, and then the least flexible job first rule (LFJF) is adopted for joint wavelength and time-slot assignment. Finally, to demonstrate the effectiveness of the proposed algorithm, a series of comparative analyses is conducted based on simulation experiments. [ABSTRACT FROM AUTHOR]

Abstract: Thermally activated delayed fluorescence materials can effectively achieve high efficiency by harvesting singlet and triplet excitons in organic light‐emitting diodes (OLEDs). However, the choice of host material has a huge impact on the efficiency of the device, especially for the near‐infrared (NIR) luminescent material. In this contribution, a series of host materials are used to match the thermally activated delayed fluorescence emitter, 3,4‐bis(4‐(diphenylamino)phenyl)acenaphtho[1,2‐b]pyrazine‐8,9‐dicarbonitrile (APDC‐DTPA), for fabricating NIR OLEDs. All the host materials have the higher triplet energy than that of APDC‐DTPA. As the organometallic compound of Zn(BTZ)2 has relatively stronger dipole moment, the electroluminescence spectral peak of doped device shows strong bathochromic shift exceeding 700 nm and changes with doping concentration. Finally, the extremely high external quantum efficiency of 7.8% (with 10 wt% of doping concentration) and 5.1% (with 20 wt% of doping concentration) are achieved with the emission peaks of 710 and 728 nm, respectively, which are superior to that of the device based on the other host materials. The approach is feasible to achieve bathochromic shift and highly efficient fluorescent OLEDs. [ABSTRACT FROM AUTHOR]

Using a phase modulator to synchronize the longitudinal modes in an all-fiber cavity, we demonstrate a wavelength tunable (1955–2045 nm) diode pumped actively mode-locked Thulium doped fiber laser with tunable repetition rate up to 10 GHz with the shortest measured pulse width of 42 ps and average output power of 5 mW. We have performed a detailed analysis of the stable mode-locking regimes, including the self mode-locking condition that challenges the harmonic mode-locked operation. We demonstrate a supermode suppression ratio of > 50 dB across the entire wavelength band of operation while maintaining a pulse width and timing jitter of < 50 ps and < 1 ps, respectively. • Wavelength and repetition rate tunable active mode-locked fiber laser at 2000 nm. • Wide wavelength tunability over 90 nm at GHz repetition rate. • Detuning performance within locking bandwidth, with intra-cavity phase modulator. • Demonstration of FM oscillation laser at 2000 nm. • Analysis of optical and RF spectra, timing jitter, stability, and pulse width. [ABSTRACT FROM AUTHOR]

Aqueous ZnSe quantum dots were synthesized by femtosecond laser ablation in microfluidics (FLAM). Hyperbranched polyethylenimine (PEI) was used to form quantum dot micelles which exhibited wavelength-tunable photoluminescence of bright visible light with the variation of pH values. The emission was attributed to the radiative deep levels introduced by the defect states. The emission peak center exhibited a blue shift as much as 25 nm to the shorter band. A possible band gap expansion mechanism for the photoluminescence wavelength tunability was discussed. [ABSTRACT FROM AUTHOR]

Fiber-based lasers and master oscillator power fiber amplifier configurations are described. These allow spectral versatility coupled with pulse width and pulse repetition rate selection in compact and efficient packages. This is enhanced through the use of nonlinear optical conversion in fibers and fiber-coupled nonlinear crystals, which can be integrated to provide all-fiber pump sources for diverse application. The advantages and disadvantages of sources based upon supercontinuum generation, stimulated Raman conversion, four-wave mixing, parametric generation and difference frequency generation, allowing spectral coverage from the UV to the mid-infrared, are considered. [ABSTRACT FROM AUTHOR]

We introduce a hybrid integration platform based on the combination of passive and electro-optic polymers. We analyze the optical and physical compatibility of these materials and describe the advantages that our hybrid platform is expected to have for the development of transmitters in terms of operation flexibility and speed. We combine our platform with InP electronics and develop a transmitter with 22-nm tunability in the C-band and potential for serial non-return-to-zero on-off-keying operation directly at 100 Gb/s. We investigate its transmission performance at 80 and 100 Gb/s using dispersion uncompensated standard single-mode fiber and demonstrate bit-error rate (BER) lower than 10−10 at 80 Gb/s after 1625 m, lower than 10−10 at 100 Gb/s after 500 m, lower than 10−9 at 100 Gb/s after 1000 m, and BER 10−7 at the same rate after 1625 m. We also employ the transmitter inside an experimental setup, which aims to emulate an optical circuit switched (OCS) domain of an intradata center network, and demonstrate at 100 Gb/s the way, in which its wavelength tunability can resolve contentions and improve the flexibility and the efficiency of the network. Finally, we outline our next plans, including the development of flexible and ultra-fast transmitters for coherent systems using the same polymer-to-polymer integration platform. [ABSTRACT FROM PUBLISHER]

On-chip 1-D photonic crystal nanocavities were designed and fabricated in a 300 mm silicon-on-insulator wafer using a CMOS-compatible process with 193 nm immersion lithography and silicon oxide planarization. High quality factors up to 105 were achieved. By changing geometrical parameters of the cavities, we also demonstrated a wide range of wavelength tunability for the cavity mode, a low insertion loss and excellent agreement with simulation results. These on-chip nanocavities with high quality factors and low modal volume, fabricated through a high-resolution and high-volume CMOS compatible platform open up new opportunities for the photonic integration community. [ABSTRACT FROM PUBLISHER]

640 Gb/s all-optical ON-OFF keying signal regeneration based on nonlinearities in a periodically poled lithium niobate (PPLN) waveguide is demonstrated and characterized. The data are transferred from the distorted original optical time division multiplexing (OTDM) signal onto a high quality and locally generated 640 GHz clock by pump depletion simultaneously operating a wavelength conversion. The thresholding behavior and the saturation effect of pump depletion in the PPLN waveguide for low and high pump power values, respectively, allow for a noise compression on the wavelength-converted replica of the original signal. The use of a stable clock with a shorter pulsewidth also allows for a sort of sampling of the original OTDM frame in the bit time center, resulting in a pulse reshaping that eliminates all noise contributions on the pulse tails. This operation produces a reduction of the original time jitter of the signal. The sampling operation also results in a compression of the new OTDM frame pulses compensating for the residual chromatic dispersion effects. After having characterized the transfer function of the proposed regeneration scheme, we evaluate its effectiveness as a function of optical signal-to-noise ratio (OSNR), pulse broadening, and time jitter of the input signal. Regeneration performance is measured in terms of bit error rate (BER) and power penalty @ BER = 10-9. Error-free operation can be recovered and maintained over an input signal OSNR range of 8 dB. This results in a BER improvement up to several orders of magnitude, obtained when the input OSNR is reduced by 20 dB with respect to the baseline. The time jitter of input signals with original jitter values from 100 to 300 fs has been reduced of nearly one order of magnitude to values lower than 40 fs. We also demonstrate that a pulse broadening up to 20% of the original pulsewidth can be compensated. Finally, wavelength tunability of the regenerator input and output signal can be, in principle, guaranteed over the whole C-band and beyond. [ABSTRACT FROM PUBLISHER]

Abstract: Conventional Raman techniques require a continuous-wave laser with stabilized wavelength, narrow line width, and sufficient output power. Due to their miniature size and low cost, diode lasers are good choice as light sources for Raman spectroscopy, especially when compact and portable instruments are needed. However, a solitary multimode diode laser has certain drawbacks that limit its use for Raman application. To circumvent these drawbacks, an external cavity can be coupled to the active gain medium of the diode to enhance the laser performance. A grating-based external cavity allows the laser to operate in a single longitudinal mode with greatly reduced line width and stabilized wavelength. This article examines the fundamentals of semiconductor lasers to show the necessity of operating diode lasers in an external cavity for Raman applications. Two feedback grating-based external cavity diode laser (ECDL) designs, viz. Littrow and Littman-Metcalf configurations, are explained. Historic and recent progress in the development of ECDL devices is reported. An updated summary of ECDL-equipped Raman systems applied to fields such as in vivo biomedical studies and in situ process/quality control is provided. Topics on mode-hop-free continuous scanning, wavelength stabilization, and dealing with ambient conditions are discussed. [ABSTRACT FROM PUBLISHER]

The current status of fiber based optical parametric oscillators is presented with a focus on pulsed systems employing microstructure fibers. It is shown based on standard expressions for parametric processes in optical fibers that systems employing short (less than a few cm) optical fibers lead to superior performance in terms of wavelength tunability and output power. Practical guidelines for realizing a working system are given. These devices are now practical as ultrafast pulsed-light sources and for extending the wavelengths of operation of existing mode-locked fiber lasers. [ABSTRACT FROM PUBLISHER]

We demonstrate group velocity dispersion (GVD) and dispersion slope (DS) compensation devices based on enhanced thermal chirping of glued fiber Bragg gratings (FBGs). By gluing a uniform FBG onto a uniform Zn channel for the GVD compensator and a linearly tapered Zn channel for the DS compensator, the thermal sensitivity of the FBG is enhanced. The thermal chirping of the FBG is given by the thermal expansion of a Zn channel, the thermooptic effect, and the thermal expansion of the optical fiber. Controlling the temperature distributions of the uniform FBG performs the tuning of GVD and/or DS, as well as their center wavelengths. These compensation devices can tune their GVD or DS while maintaining a constant center wavelength and change their center wavelengths while preserving constant GVD or DS values. The GVD can be tuned from -123.39 to -57.29 ps/nm with the center wavelength at 1552.9 nm, while the center wavelength can be shifted 2.2 nm with a GVD value of about -105 ps/nm. On the other hand, the DS can be tuned from -8.88 to -24.44 ps/nm2 with the center wavelength at 1554.5 nm, while the center wavelength can be shifted 0.6 nm with a DS value of about -10.4 ps/nm2. [ABSTRACT FROM PUBLISHER]

We demonstrate wide bandwidth operation in a semiconductor optical amplifier (SOA)-based fiber laser with a wavelength spacing of 25 GHz. A broadband multiwavelength filter based on superimposed and chirped fiber Bragg gratings is used for wavelength selection. Three different cavity configurations are presented and compared: 1) a single-SOA standing-wave cavity; 2) a single-SOA ring cavity; and 3) a double-SOA ring cavity. Up to 41 wavelengths are obtained with a signal-to-noise ratio of 35 dB and a wavelength tunability of 10 nm. [ABSTRACT FROM PUBLISHER]

All-optical flip-flop operation using external optical control is demonstrated in a single semiconductor optical amplifier (SOA)-based fiber ring laser with an intracavity Lyot filter. Its operation is based on the principle of cross-gain saturation in the SOA. A unique feature of this flip-flop is its ability to be set and reset at multiple wavelength pairs of an auxiliary continuous wave control light that is injected into the fiber ring cavity; this, together with the wide wavelength tunability of the Lyot filter makes the flip-flop potentially useful in wavelength-division multiplexing applications. Bistable output at 1571 nm with a contrast ratio of 20 dB between the two output power states of the flip-flop using -3 dBm power of the external optical control is demonstrated [ABSTRACT FROM PUBLISHER]

The article presents a joint-transform phase correlator with a sharp correlation peaks produced by the numerical Fourier transformation of a phase in a joint-power spectrum. The phase can be measured by six-step phase-shifting interferomety with a tunable laser-diode (LD). The algorithm in six steps is not sensitive to the LD power alterations. A best discrimination performance can be obtained from the phase correlator. Calculation results were also presented.

All-optical wavelength conversion and multicasting with input and output wavelength tunability is a desired component for reconfigurable wavelength-division-multiplexed (WDM) networks for improving the efficiency and performance. In this paper, we propose a novel tunable all-optical wavelength-conversion-and-wavelength-multicasting schemes by using orthogonally polarized nondegenerate four-wave mixing (FWM) in highly nonlinear fiber. The input signal is amplified and serves as one of the two pumps. Wide tunability is obtained by placing a dummy pump and dummy signals at appropriate wavelengths with respect to the input wavelength and desired output wavelengths. For a 10-Gb/s NRZ system, 1:3 multicasting is demonstrated with a less than 0.6-dB power penalty, over a 25-nm tuning range for both input and output signals. [ABSTRACT FROM PUBLISHER]

Three existing wavelength monitor integrated laser module designs are evaluated. The shortcomings of these designs are resolved by a unique design that eases alignment tasks and greatly enhances the wavelength stability and the wavelength tunability. For example, the wavelength drift over case temperature is 16 times smaller than the best result of previous reports. With the incorporation of thermal compensation, the temperature-induced wavelength drift of the etalon is eliminated. In anticipation, this design enables a worst overall wavelength-drift of 4.41 pm after 25 years of usage to be achieved. [ABSTRACT FROM PUBLISHER]

State-of-the-art distributed feedback (DFB) laser modules integrated with a wavelength monitor are presented that provide excellent wavelength stability. By adopting unique and compact configuration, wavelength deviations of as small as a few picometers have been achieved. The laser modules are improved also in the scope of high power, high reliability, and wavelength tunability. Reliability test results of the DFB laser diodes and modules confirm a sufficiently long lifetime of more than 25 years and a small wavelength drift of less than ±3 pm. The developed laser modules are fully applicable to ultradense wavelength-division multiplexing applications with the current narrowest channel spacing of 25 GHz. [ABSTRACT FROM PUBLISHER]

A p-type Ge quantum dot infrared photodetector is investigated in this paper. The intrinsic thick Si layers are utilized to block the dark current under low bias and adjust the tunneling probability by controlling applied field to tune the responsivity spectrum. The 30 K responsivity spectrum shows broadband from 2 to 9 μm at zero bias with photovoltaic effect and extends its range to 20 μm when the applied bias is increased.For long wavelength detection, our detector is tunable with Si blocking layer. The detectivity in this sample has maximum value toward 2.1 × 1010 cm (Hz0.5)/W under 0.2 V for the 6 μm wavelength. That for the long wavelength is ∼109 cm (Hz0.5)/W. [Copyright &y& Elsevier]

For a wavelength division multiaccess (WDMA) system, the reservation (R-WDMA) and the preallocation (P-WDMA) protocols are two major media access methods to support packet-switched traffic. In this paper, a new media access control (MAC) protocol, accelerative preallocation WDMA (AP-WDMA), is proposed to overcome the disadvantages of P-WDMA and retain its advantages. AP-WDMA relieves the technology constraints by restricting the wavelength tunability at only one end of the communication link, removes the channel and station status tables required by R-WDMA, and uses simple arithmetics to allocate channels. Although it uses a dedicated control channel to send control-acknowledge packets, AP-WDMA employs a network management mechanism to make full use of idle time slots under different propagation and tuning delays. In addition, it is well suited to wavelength-limited networks. Three heuristic methods for channel sharing, interleaved (I), neighborhood (N), and weighted-balanced (WBH), are evaluated. Through analytical evaluations, AP-WDMA is shown to be able to improve the channel utilization and system throughput much more significantly than I-TDMA*, which is a P-WDMA protocol. We also evaluate the impact on the performance of AP-WDMA by the number of channels, the four traffic types (mesh, disconnected, ring, and uniform), the degree of channel sharing, and the unbalanced load among channels. The results show that the utilization is scalable in terms of the number of channels. Furthermore, the utilization of channels is best for the ring-traffic type and worst for the disconnected-traffic type, and the system throughput decreases as the degree of channel sharing increases. Finally, using heuristics I or WBH instead of N can resolve the unbalanced load problem under various traffic types and degrees of channel sharing [ABSTRACT FROM PUBLISHER]

The wavelength tunability and the polarization characteristics of twisted polarization beamsplitting fiber couplers are investigated experimentally and analyzed theoretically. The measured spectrum transmissions and polarization characteristics agree well with the theoretical results. The wavelength working as a polarization beamsplitter can be tuned in the 1.3-1.75 μm wavelength range without significant degradation. Splitting ratios for orthogonally polarized light are more than 20 dB and less than -20 dB [ABSTRACT FROM PUBLISHER]

We demonstrate step-tunable single-mode operation of a gain-switched diode laser by nonresonant self-injection seeding from an uncoated glass slide used as an external cavity reflector. A spectral bandwidth reduction from 11 nm to 0.05 nm and wavelength tunability has been achieved for picosecond (near-transform-limited) pulses with little effect on other laser characteristics. Good agreement with numerical simulations based on a compound-cavity laser model is also reported [ABSTRACT FROM PUBLISHER]

Broad-band tunability of erbium-doped silica fiber ring lasers in the 1.48-1.62 μm wavelength band is demonstrated through modeling and experiment. Tunability over the erbium-doped fiber amplifier (EDFA) C- and L-bands is achieved with a simple laser design using a single gain medium working in deep saturation. A comprehensive numerical model based on an iterative solution of propagation rate equations and spectrally resolved Giles parameters was used to analyze the impact of various laser variables. The dependence of laser output power on total cavity loss, erbium-doped fiber length, pump power, and lasing wavelength has been investigated. The calculated laser characteristics have been found in good quantitative agreement with the experimentally obtained data. Experimental results concerning wavelength tunability, output power, and lasing wavelength repeatability/stability and spectral purity are also presented [ABSTRACT FROM PUBLISHER]

Laser diodes (LDs) have been applied to a phase-measuring interferometer through the wavelength tunability of LDs by controlling their currents. Laser-diode interferometers based on a heterodyne technique are reviewed. A two-wavelength laser-diode interferometer is demonstrated with current control of dual LDs in opposite directions. A synthetic wavelength makes it possible to extend the range of interferometric measurements. The wavelength is controlled by the laser injection current and is stepwise or rampwise changed to introduce a time-varying phase difference between the two beams of an interferometer with unbalanced optical path lengths. The optical output is demodulated with a phase-extraction algorithm. Systematic phase errors caused by the LD-power variation and by the difference between the beat frequency and ramp frequency are analyzed. A feedback interferometer with electronics is used to eliminate the phase error by locking the interferometer on a preset phase. Typical experimental results are shown. [ABSTRACT FROM AUTHOR]

A wavelength-tunable high repetition rate (HRR) erbium-doped fiber laser in L-band based on dissipative four-wave mixing (DFWM) mechanism is demonstrated. The cavity can generate a single-soliton train and bound-soliton train with a fixed repetition rate of ~126 GHz, which is determined by the free spectral range of the intra-cavity Lyot filter. A wide wavelength-tuning operation can also be obtained by rotating the polarization controllers. The wavelength-tuning ranges of the HRR single-soliton state and HRR bound-soliton state are ~38.3 nm and ~22.6 nm, respectively. This laser provides useful references for the area of a wavelength-tunable fiber laser with high repetition rate. The laser may also find useful applications in high-speed communication, sensing, etc. [ABSTRACT FROM AUTHOR]

A perovskite microlaser is potentially valuable for integrated photonics due to its excellent properties. The artificial microlasers were mostly made on polycrystalline films. Though a perovskite single crystal has significantly improved properties in comparison with its polycrystalline counterpart, an artificial microlaser based on single-crystal perovskite has been much less explored due to the difficulty in producing an ultrathin-single-crystal (UTSC) film. Here we show a device processing based on a perovskite UTSC film, confirming the high performance of the UTSC device with a quality factor of 1250. The single-crystal device shows 4.5 times the quality factor and 8 times the radiation intensity in comparison with its polycrystalline counterpart. The experiment first proved that hybrid perovskite microlasers with a subwavelength fine structure can be processed by focused ion beams (FIB). In addition, a wavelength-tunable distributed feedback (DFB) laser is demonstrated, with a tuning range of ∼4.6 nm. The research provides an easily applicable approach for perovskite photonic devices with excellent performance.

Abstract: A compact current sensor using a microfiber knot resonator (MKR) is demonstrated. With the assistance of a copper wire that is wrapped by the microfiber knot, resonant wavelength inside the MKR can be tuned by applying electric current to the copper wire. The resonant wavelength change is based on the thermally induced optical phase shift in the MKR due to the heat produced by the flow of electric current over a short transit length. It is shown that the wavelength shift is linearly proportional to the square of the amount of current and the maximum tuning slope of 51.3pm/A2 is achieved using a newly fabricated MKR. [Copyright &y& Elsevier]

A scheme is proposed for tunable all-optical format conversion from BPSK to OOK signal without active phase locking under the highly nonlinear loop structure. The 20 Gbit/s BPSK is mapped to two-level amplitude signal by delay interferometer (DI). One carrier branch generated locally remodulates the amplitude information to phase based on cross-phase modulation (XPM) effect in the highly nonlinear fiber (HNLF). The other carrier propagates as a pump under symmetrical loop ensuring the stability of phase relationship. After interference and vector shifting in coupler, the wavelength-tunable OOK is obtained. Benefiting from the signal remodulation mechanism and symmetric loop setup, separate carrier extraction and additional phase-locking are not required. The feasibility of the scheme is demonstrated by constellation diagram, eye diagram and pattern transformation diagram in numerical simulations. At the BER of 10 − 3 , the converted OOK has ∼ 0.7 dB and ∼ 1.9 dB optical signal-to-noise ratio (OSNR) improvement, respectively, compared to back-to-back (B2B) OOK under different quality of input signals. It is shown that the scheme optimizes the signal quality while converting signal formats. For low-quality BPSK with OSNR of 15 dB, the system indicates better noise tolerance. Furthermore, the scheme has potential scalability to bidirectional format conversion between BPSK and OOK. • A phase-locking free scheme for phase erasure and format conversion of BPSK signal is proposed. • The OSNR performance is improved obviously while converting format. • Wavelength tunable conversion enhances flexibility of the system based on Highly Nonlinear Optical Loop Mirror. • The potential scalability to bi-directional format conversion is analyzed. [ABSTRACT FROM AUTHOR]

Mode-locked erbium-doped fiber laser with a full L-band wavelength tunability from 1567 to 1612 nm by controlling the ratio of its output coupler is demonstrated, which exhibits intracavity gain of 34 dB and maximum output power of 91 mW. The dual-wavelength (980 and 1480 nm) bidirectional pumping scheme enhances quantum efficiency and power conversion ratio to 42% and 37%, respectively. Continuous-wave lasing linewidth of 0.02 nm is obtained with the introduction of an intracavity air-gap Fabry-Peacuterot filter made by polishing the fiber connector end. A 45-nm wavelength tunablility with pulsewidth of 2.4 ps and linewidth of 6.8 nm are observed under mode-locking regime. Tuning resolution of 0.3 nm and wavelength-dependent power variation of <1.2 dB are also reported [ABSTRACT FROM PUBLISHER]

An optical high-frequency pulse generation method with wavelength tunability is presented by taking advantage of vernier-type gratings in a distributed Bragg reflector laser diode. Experimental results showed that sinusoidal optical pulses, whose lasing wavelengths were tunable, were created with repetition frequencies around 30 GHz. The widths of the radio frequency spectra, furthermore, were drastically reduced by means of mode locking with externally injected optical pulses. [ABSTRACT FROM PUBLISHER]

We demonstrate a microstructure-fiber (MF)-based supercontinuum source and a synchronously pumped optical parametric oscillator in the 1550-nm regime. By using a 12.5-m-long MF, we obtained a 10-GHz repetition-rate picosecond-pulse source that is capable of ∼120-nm wavelength tunability due to the wide-gain bandwidth of the combined processes of stimulated Raman scattering and parametric four-wave mixing. [ABSTRACT FROM PUBLISHER]

We demonstrate a dispersion compensation device based on thermal chirping of a glued fiber Bragg grating. The device can change the group velocity dispersion (GVD) while maintaining a center wavelength or change the center wavelength while preserving a GVD value. The GVD can be tuned from -122.5 to -57 ps/nm with a center wavelength at 1552.9 nm. On the other hand, the center wavelength can be shifted by 2.2 nm with a GVD value around -105 ps/nm. [ABSTRACT FROM PUBLISHER]

Thermally activated delayed fluorescent (TADF) emitters have received great attention in organic light-emitting diodes and laser diodes because of high exciton utilization efficiency and low optical loss caused by triplets. However, the direct observation of lasing emission from nondoped TADF microcrystals has yet to be reported. Here, we demonstrated a three-color (green, yellow, and red) microlaser from three nondoped TADF microcrystals with well-controlled geometries. The temperature-dependent dynamic analyses testify that the regenerated singlets which originated from the reverse intersystem crossing process at room temperature are beneficial for population inversion and reduce triplet-absorption/annihilation optical loses, together resulting in thermally activated lasing actions. Thanks to single-crystalline structures of TADF emitters, the relationship between triplet-harvesting capability and the molecular structure was systematically investigated. The results not only offer rational design of pure TADF gain materials but also provide guidance for the high-performance electrically driven organic solid-state lasers and multicolor laser integration.

Frequency doubling of a Ti:sapphire laser with a KNbO crystal has been used to generate wavelength tunable amplitude-squeezed lights in the second harmonic mode. The crystal is placed in an enhancement cavity designed to resonate only the fundamental mode, and the phase matching condition is achieved by changing the crystal temperature. Noise reduction of 1.8-2.0 dB below the shot noise level is observed between 427.28 and 433.76 nm. [ABSTRACT FROM AUTHOR]

A Bragg grating in a single-mode polymer optical fiber (POF) has been created. The novel grating has a length of 1 cm with a reflectivity of 80% and a linewidth of about 0.5 nm. The wavelength tunability of the POF grating by stretching was investigated and a wavelength tunable range of 20 nm has been achieved. Based on the properties of the polymer, we believe that this kind of grating has a wavelength tuning potential of more than 100 nm [ABSTRACT FROM PUBLISHER]