Real-time Wavelength Research Articles

Wearable quantum dots organic light-emitting diodes patch for high-power near infra-red photomedicene with real-time wavelength control

Wearable photomedical application fields, such as photobiomodulation (PBM), and photoplethysmography (PPG) sensors using organic light-emitting diodes (OLEDs), are promising and attractive due to their flexibility, surface light emission, and ability to apply to various free-form (attachable or implantable) healthcare platforms. However, to maximize the impact on wearable photomedical applications, their spectrum needs to be freely tunable in real-time, and expanded into the near-infrared (NIR) wavelengths which are difficult to achieve in conventional electroluminescent OLED. In this study, we introduce the wavelength selective quantum dots high-power parallel-stacked OLED (QD-OLED) patch. Several NIR QD-OLEDs with 630, 700, and 730 nm peak wavlength were optimized by the high-power (> 100 mW·cm−2 at 6.3 V) parallel-stacked blue OLED with a 465 nm emission peak.The NIR QD-OLED patch platform with multi-functional blue reflective NIR-enhanced (> 60 %) encapsulation film (6 x 10−6 g·m−2·day−1), capable of real-time wavelength control, achieved a high-output NIR power density (>23.28 mW·cm−2). Using this NIR QD-OLED patch, PPG bio-signals were successfully measured. Additionally, this NIR QD-OLED demonstrated that it can increase the proliferation of dermal papilla cells by up to 131 % through NIR wavelength control, thereby optimizing the hair growth effect.

Analog Wavelength Locking in an Optical Single-Sideband Transmitter of a Millimeter-Wave Radio-Over-Fiber Link Featuring a Micro-Ring Resonator and a Heat-Pump-Controlled Laser

This paper presents a novel approach to addressing the issue of temperature-induced instability in an optical, single-sideband transmitter based on a micro-ring resonator (MRR) suitable for millimeter-wave (mmW) radio-over-fiber (RoF) communications. We propose utilizing the drop port of the MRR to provide a feedback signal to the closed-loop control (CLC) system. The latter serves to maintain the optimal alignment between the laser’s carrier and the MRR’s resonant wavelength, thus mitigating the adverse effects of chromatic-dispersion-induced power fading at the receiving end. Since the feedback information is extracted from the otherwise-wasted resonant energy at the drop port, the control system does not compromise the delicate optical signal at the through port. A CLC was synthesized, designed, and prototyped to provide real-time wavelength tuning of the heat-pump-controlled laser based on the feedback signal. Experimental evaluations demonstrate that the wavelength of the laser could be successfully locked to the MRR’s resonance with a wavelength dither of less than 0.004 nm (~491 MHz). This allowed us to limit the power-penalty deterioration to less than 2 dB for a RoF link with a 2.5-km standard telecommunication single-mode fiber (SMF), a modulation frequency of 37.8 GHz, and a carrier wavelength of 1563.97 nm (~191.820 THz). The proposed solution offers an alternative approach for the carrier and the MRR’s resonant wavelength interlocking without the need for complex photonics like thermo-optic or electro-optic structures to control the temperature or phase velocity, respectively.

Real‐Time Superresolution Interferometric Measurement Enabled by Structured Nonlinear Optics (Laser Photonics Rev. 17(6)/2023)

A Structured-Light Enabled Nonlinear Interferometer In article number 2200967, Zhi-Han Zhu, Xiao-Peng Hu, Bao-Sen Shi, and colleagues describe a structured-light enabled nonlinear interferometer capable of superresolution measurement in real time. Such a novel technique realized the first observation of a 12-photon de Broglie wavelength in real time by using only a low-cost detector, providing a promising new way for the development of superresolution interferometric metrology.

Seawater Temperature Measurement System Based on Wavelength Sweeping and Cross Correlation Algorithm

A real-time seawater temperature measurement system based on a wavelength swept distributed feedback laser is developed. The π phase shifted Fiber Bragg grating with a narrow bandwidth of 12 pm is used as the sensing probe. The wavelength is swept by linearly and periodically modulating the driving current of laser with a sawtooth wave signal. The absorption line of H13C14N gas cell provides a standard wavelength to calibrate the swept wavelength in real time to reduces the measurement error induced by the noises or drifts of the laser. Resonance difference between the measurement and the reference in time domain is obtained via a series of digital signal processing such as normalization, derivation, low-pass filtering and cross-correlation operation. Experimental results show that, the sensitivity of the sensor is 16.22 pm/°C, the dynamic range is about 55 °C, the resolution is as high as 0.002 °C, and the thermal response time is ~50 ms. The sensor system is compact, simple, high-resolution and large-dynamic range that has potential application for ocean temperature monitoring.

Directional amplified spontaneous emissions from Ag nanohole array with high diffraction orders.

Surface plasmon excitations in metallic hole arrays have been extensively studied in the context of light-matter interaction, since the generated Bloch surface plasmon polariton (Bloch-SPP) exhibits unique properties of nanoscale light confinement, near-field enhancements, and long-range metal surface propagation. In this work, we experimentally demonstrate a plasmonic device that exhibits highly directional emission in visible light; using Ag film with a thickness of 100 nm deposited on a subwavelength porous alumina array as a plasmonic cavity, four-level rhodamine 6G (R6G) is selected as the gain material. It is suggested that a Bloch-SPP with high diffraction orders on a Ag nanohole array can generate a strong local electric field and a high Purcell factor at a nanohole edge. Moreover, directional five-fold enhanced amplified spontaneous emission (ASE) with polarization dependence is observed under a low threshold of 199.9 W/cm2 in the visible light region, which comes from the optical feedback provided by the 2D periodic nanohole array. This work opens up a wide range of applications for real-time tunable wavelength, controlled multimode laser, fluorescence detection, etc.

High-Speed and High-Resolution Optical Fiber Sensor Interrogation Based on Optical Injection in Semiconductor Laser and Microwave Filtering

Real-time and high-speed interrogation of optical fiber sensors normally requires sophisticated detection systems. Here a novel microwave photonic approach for interrogation of high-speed and high-resolution optical fiber sensors based on optical injection in a semiconductor laser and simple passive microwave frequency filtering is proposed and experimentally demonstrated. An intensity-modulated master laser is injected into a semiconductor laser to produce a wavelength scanning optical sideband. A fiber Bragg grating (FBG) sensor is embedded into a fiber ring laser. Beating of the scanning optical sideband and the fiber ring laser wavelength at a photodetector generates a linearly frequency-chirped microwave signal. The real-time wavelength shift of the FBG sensor is converted into the change of the microwave center frequency. After a simple passive microwave bandpass filter, two electrical pulses are obtained corresponding to positive and negative frequency sweeping. The FBG wavelength can be retrieved from the time interval of the two pulses. A proof-of-concept experiment to measure an FBG strain sensor has been carried out. A high interrogation speed of 1 MHz and measurement sensitivity of 17.3 ns/μϵ have been achieved.

A miniaturized, low-cost and portable fiber Bragg grating interrogation system for remote monitoring

A miniaturized, low-cost, 4-channel fiber Bragg grating (FBG) interrogation system for real-time remote monitoring is presented in this paper. A superluminescent light emitting diode (SLED) as the broadband light source combined with an interrogation module and an optical switch is applied in the system. The moving average method is employed to remove noise effects, and then Gaussian fitting method is used to realize the interrogation of FBG central wavelength with high precision. On software design, the WebSocket network protocol is introduced to establish communication between data processing core and webpages to achieve cross-platform remote access through the browser without user’s software installation. The proposed interrogation system not only displays the reflected spectrum and demodulated central wavelength in real time on the webpage, but also realizes the data storage and channel switch remotely. The interrogator for remote monitoring of FBG sensors proposed in this paper has been proved experimentally with the interrogation resolution 0.1 pm, the precision of 5 pm for the FBG central wavelength, interrogation stability up to ± 1.1 pm, and interrogation frequency of 4 kHz.

Thermal effect induced dynamically lasing mode tuning in GaN whispering gallery microcavities

Thermal modulated real-time wavelength tuning of semiconductors has shown great potential for GaN-based sensors or photo-electricity modulators. Herein, we study the temperature mediated photoluminescence (PL) properties in GaN materials via PL and time-resolved PL measurement in situ and synchronously. We then broaden the phenomenon to lasing mode tuning of whispering gallery cavities. To understand the underling mechanism, time, and frequency domain properties of spontaneous emission from GaN film, amplified spontaneous emission and stimulated emission from floating GaN microdisks in a temperature region from 0 °C to 50 °C are compared. According to analysis of temperature-related changes in the central wavelength, peak intensity, full width at half maximum (FWHM), and carrier dynamics, the thermal controlled PL properties of various structures are well understood. Material structure-related changes in exciton combination channels and temperature-related changes in central wavelength, peak intensity, FWHM, and exciton combination times are observed. Finally, real-time lasing mode modulation in floating GaN microdisks is realized. Our work reveals the lasing tuning method in situ, implying a promising strategy for fabricating high performance thermal-optic modulation devices.

Real-time dynamic wavelength tuning and intensity modulation of metal-clad nanolasers.

To realize ubiquitously used photonic integrated circuits, on-chip nanoscale sources are essential components. Subwavelength nanolasers, especially those based on a metal-clad design, already possess many desirable attributes for an on-chip source such as low thresholds, room-temperature operation and ultra-small footprints accompanied by electromagnetic isolation at pitch sizes down to ∼50 nm. Another valuable characteristic for a source would be control over its emission wavelength and intensity in real-time. Most efforts on tuning/modulation thus far report static changes based on irreversible techniques not suited for high-speed operation. In this study, we demonstrate in-situ dynamical tuning of the emission wavelength of a metallo-dielectric nanolaser at room temperature by applying an external DC electric field. Using an AC electric field, we show that it is also possible to modulate the output intensity of the nanolaser at high speeds. The nanolaser's emission wavelength in the telecom band can be altered by as much as 8.35 nm with a tuning sensitivity of ∼1.01 nm/V. Additionally, the output intensity can be attenuated by up to 89%, a contrast sufficient for digital data communication purposes. Finally, we achieve an intensity modulation speed up to 400 MHz, limited only by the photodetector bandwidth used in this study, which underlines the capability of high-speed operation via this method. This is the first demonstration of a telecom band nanolaser source with dynamic spectral tuning and intensity modulation based on an external E-field to the best of our knowledge.

Fast Demodulation of Fiber Bragg Grating Wavelength From Low-Resolution Spectral Measurements Using Buneman Frequency Estimation

This paper presents a fast demodulation algorithm to determine fiber Bragg grating (FBG) from spectra acquired by low wavelength resolution spectrometers. A modified and improved Buneman frequency estimation algorithm is employed in tracking FBG wavelength and eliminating FBG wavelength discontinuities in real-time wavelength demodulation calculations. The FBG demodulation algorithm was tested using a 512-element detector array spectrometer with a 156 pm/element resolution. At a 2-kHz spectrum acquisition rate, the demodulation algorithm achieved a 0.048 pm Bragg wavelength resolution. The computational efficiency and robustness of the new algorithm was compared with a Gaussian FBG peak fitting method. Our method provides a real-time demodulation scheme to track FBG wavelength using low-resolution spectrometers or tunable lasers. It has the potential to significantly reduce the cost of FBG interrogation systems that are employed in high-sensitivity and high-speed sensing applications.

Real-time 400 Gbps/carrier WDM transmission over 2,000 km of field-installed G.654.E fiber.

We combine erbium-doped fiber amplifier (EDFA) and backward distributed Raman amplifier (DRA) to achieve the real-time wavelength division multiplexing (WDM) transmission of 400 Gbps/carrier polarization division multiplexing (PDM) 16 quadrature amplitude modulation (QAM) signals over 2,000 km of terrestrial field-deployed cut-off shifted fiber (CSF) compliant with ITU-T G.654.E. This paper compares the transmission performance of 400 Gbps/carrier signals achieved in CSF and standard single-mode fiber (SMF). This transmission distance, 2,019 km, is, to the best of our knowledge, the longest in 400 Gbps/carrier WDM transmission field experiments using digital signal processing (DSP) application specific integrated circuit (ASIC) integrated real-time optical transponders with the technologies to compensate device imperfections; the backward DRA used is fully compliant with laser power safety requirements.

Focus on photonics, spectrometry, and spectroscopy

Focus on photonics, spectrometry, and spectroscopy

Real-time wavelength routing based on Bragg reflection with integrated forward Raman for long-reach networks

We experimentally demonstrate the all-optical efficient technique for dynamic full-duplex wavelength routing and reach extension through adoption of passive fibre Bragg grating (FBG), energy efficient vertical cavity surface emitting lasers (VCSELs) and high gain forward Raman pump. In this study, two VCSEL channels at 1 549.62 nm and 1 550.01 nm are directly modulated with a 8.5 Gbit/s data signal each, and transmitted over 25.5 km fibre to a passive single mode FBG-based wavelength routing node. The precise wavelength selectivity of the FBG is exploited to achieve all-optical real-time wavelength routing of the 1 549.62 nm VCSEL channel with a maximum insertion loss of 22.1 dB. The 1 550.01 nm channel is transmitted through the FBG with a maximum penalty of 1.03 dB. By utilizing the 7.2 dB flat gain of a forward Raman pump, the routed 1 549.62 nm VCSEL channel is transmitted over 76.7 km fibre with a maximum penalty of 3.84 dB at bit error rate (BER) of 5−5. Our technique is all-optical, power efficient as it employs passive FBG and circulators and has low cross talk allied to precise wavelength selectivity of the technique.

Real-Time Correction and Stabilization of Laser Diode Wavelength in Miniature Homodyne Interferometer for Long-Stroke Micro/Nano Positioning Stage Metrology.

A low-cost miniature homodyne interferometer (MHI) with self-wavelength correction and self-wavelength stabilization is proposed for long-stroke micro/nano positioning stage metrology. In this interferometer, the displacement measurement is based on the analysis of homodyne interferometer fringe pattern. In order to miniaturize the interferometer size, a low-cost and small-sized laser diode is adopted as the laser source. The accuracy of the laser diode wavelength is real-time corrected by the proposed wavelength corrector using a modified wavelength calculation equation. The variation of the laser diode wavelength is suppressed by a real-time wavelength stabilizer, which is based on the principle of laser beam drift compensation and the principle of automatic temperature control. The optical configuration of the proposed MHI is proposed. The methods of displacement measurement, wavelength correction, and wavelength stabilization are depicted in detail. A laboratory-built prototype of the MHI is constructed, and experiments are carried out to demonstrate the feasibility of the proposed wavelength correction and stabilization methods.

Real-time wavelength reuse based on Bragg trans-reflection for dynamic reference frequency and data transfer in Datacom

ABSTRACTWe experimentally demonstrate the first VCSEL-based all-optical wavelength reuse technique with reconfigurable fibre Bragg grating add and drop multiplexer. EDFA gain saturation and Bragg trans-reflection effect on a single FBG are respectively, adopted for full-duplex reference frequency and data transfer. A 1550 nm energy-efficient VCSEL is modulated with 1.7 GHz clock signal and transferred downstream over 26.6 km fibre OLT attain a phase noise stability of −54.01 dBc/Hz at 10 kHz offset frequency. A saturated EDFA is exploited to optically reduce the peak-to-peak voltage of the incoming downstream RF, allowing for wavelength reuse with 10 Gbps upstream data. A 1.57 dB transmission penalty is incurred over the transmission fibre. An all-passive OADM is developed exploiting Bragg trans-reflection at 1549.45 nm. The reflected wavelength is routed over another 24.7 km fibre network attaining an extinction ratio of 6.1 dB and a SNR of 5.8 dB. This work provides an all-optical technique for routing and spectral management in flexible networks.

Current Profile Reconstruction Using Motional Stark Effect Polarimeter Data on HL-2A Tokamak

In order to reconstruct the plasma current density, the Current Profile Fitting (CPF) code has been successfully developed on the HL-2A tokamak. A seven-channel motional Stark effect (MSE) diagnostic based on dual photoelastic modulators is installed to measure the pitch angle of the magnetic field, which can be used as an internal magnetic field constraint for the CPF code. Recently, the MSE polarimeter was upgraded with a real-time wavelength matching system to improve the signal-to-noise ratio. The magnetic field angle (γpitch) with a temporal resolution of 10 ms can be provided. In the CPF code, the plasma current density is described as a polynomial, and the Least-Squares method is used to determine the coefficients of the polynomial. The Finite Difference method and the Strongly Implicit Procedure method are used to solve the Grad-Shafranov equation. The code operation is stable. With the improved-quality MSE data, the CPF calculation result of shot 30782 suggests that the safety factor q profile is monotonic. The minimum q value is less than 1 on-axis during sawtooth oscillations in shot 30782. And, the position of the q = 1 surface is consistent with the sawtooth inversion radius measured by electron cyclotron emission and soft X-ray diagnostics.

Real-time 850 nm multimode VCSEL to 1 550 nm single mode VCSEL data routing for optical interconnects

Short-reach optical interconnects among massive serves in data centers have attracted extensive research recently. Increasing capacity, cost and power efficiency as well as wavelength switching between data center network nodes are still key challenges for current optical interconnects. In this work, we experimentally demonstrate the real-time inter-mode optical wavelength switching technique, for high-speed wavelength flexible data center interconnects. A 10 Gbit/s 1 550 nm single mode vertical cavity surface emitting laser (VCSEL) is optically injected and used to control a 10 Gbit/s multimode VCSEL carrier at 850 nm. Results show that a clearly open eye diagram is achieved at back-to-back analysis, implying a successful wavelength switch and error-free operation at 10 Gbit/s. A fully optical wavelength conversion of a multimode VCSEL operation at 850 nm using a single mode VCSEL subject to external optical injection at 1 550 nm is reported. This work opens new perspectives towards the development of a cost effective high-speed real-time inter-band wavelength switching technique between servers and network devices operating at different transmission windows at network nodes, for current and future optical interconnects.

VCSEL-based broadband wavelength converter for ultra-wideband flexible spectrum data routing in optical interconnects

Abstract High-speed real-time wavelength conversion at key data centre network nodes is an emerging fundamental functionality requirement for transparent content resolution, wavelength assignment and routing towards better utilization of network resources under dynamic traffic patterns. In this paper, we experimentally demonstrate the first vertical cavity surface emitting laser (VCSEL)-based broadband wavelength converter for ultra-wide wavelength routing in Datacom. An 850 nm multimode VCSEL is directly modulated with 8.5 Gbps data and successfully transmitted error-free over 100 m OM3 multimode fibre (MMF) with a receiver sensitivity of −16.04 dBm, and a total transmission penalty of 1.14 dB. The received data is then used to run two cascaded single mode VCSELs at 1550 nm within the network integration node, therefore achieving the first reported real-time inter-band wavelength converter to C-band. By exploiting VCSEL wavelength tuneability with changing bias current, we show that the converted wavelengths can be routed over 3.2 nm spectra range for integration into ITU-T 50 GHz flexible grid and beyond. The newly converted wavelengths are successfully transmitted over 24.7 km of G 655 single mode fibre, achieving a minimum receiver sensitivity of −14.28 dBm, with a maximum transmission penalty of 2.72 dB. This work offers a viable enabling development technology for broadband wavelength converters for real-time wavelength routing in optical interconnects to address content resolution and wavelength assignment problem for current and future Datacom.

A highly precise FBG sensor interrogation system with wavemeter calibration

Abstract Fiber Bragg grating (FBG) demodulators based on tunable lasers have been extensively applied in many fields. However, the tunable lasers can hardly avoid wavelength nonlinear tuning. Such problems and unexpected wavelength fluctuations may cause serious measurement errors. In this study, we propose a wavelength calibration scheme to solve this problem by incorporating a magneto-optic wavemeter into the interrogation system. We present experimental verification of real-time wavelength calibration of tunable lasers and measurement corrections. In the temperature measurement demonstrations, the experimental results show that the FBG interrogation accuracy was raised from ±3 pm to ±1 pm, and better long-term stability was achieved, corresponding to the temperature accuracy of ±0.1 °C.

Note: Real-time wavelength matching system designed for the motional Stark effect polarimeter on HL-2A tokamak.

A 7-channel motional Stark effect diagnostic based on dual photo-elastic modulators is installed and operated routinely for rather low beam energy and magnetic field on the HL-2A tokamak, with a spatial resolution of ∼3 cm and a temporal resolution of 10 ms. The instrument observes the σ component of the full energy Dα from the first or the fourth ion source of a neutral beam injector. However, the change in beam energy during a discharge causes variation of the Doppler shift with the maximum of 1 Å, which leads to the polarization fraction drop from 30%-40% to 10% and then makes the signal-to-noise ratio of the system become very poor. Therefore, a real-time wavelength matching system is designed to promote polarization fraction. The beam emission spectra are filtered by using a monochrometer in real time. And a narrowband filter is tilted by using an absolutely calibrated rotator through beam energy in order to make sure that the deviation of wavelength matching is less than 0.1 Å.