Wavelength-selective Components Research Articles

Gain-Switched Er-Doped Fluoride Fiber Laser at ~3.75 μm

We demonstrate a pulsed Er-doped ZBLAN fiber laser operating at 3.75 μm based on the gain-switching scheme. A diffraction grating is introduced as a wavelength selection component to enable stable lasing in this long-wavelength region that deviates from the emission peak of 4F9/2→4I9/2 transition in Er3+. Different from the conventional gain-switching behavior where the pulse repetition frequency of the output laser is same as the that of the pump, the gain-switched laser demonstrated here shows a variable pulse repetition frequency, which accounts for 1/n (n = 4, 3, 2) of the pump pulse repetition frequency, in response to the 1950 nm pump power. The output pulse characteristics, including average output power, repetition frequency, pulse duration, and peak power, are investigated in detail. Over 200 mW average output power at 3.75 μm was obtained at 12 W of 1950 nm pump power. This work demonstrates that the Er-doped ZBLAN fiber laser, in combination with gain-switched scheme, is a feasible and promising approach to generate powerful pulsed emission > 3.7 μm.

Enhancing sensitivity of trace copper detection based on coupled optoelectronic oscillator

We propose to employ coupled optoelectronic oscillator (COEO) for trace copper detection to achieve an enhanced sensitivity and stability. By replacing the optical source of the traditional OEO with an optical feedback loop, the oscillation frequency is determined by the cavity loop length in conjunction with the laser output wavelength. The sensing head, which is fabricated by inserting a fusion spliced fiber with large lateral offset fusion splicing in a Sagnac loop, act as a wavelength selection component in the laser loop. Hence, the oscillation frequency changes with the varying solution concentration. Benefitting from the matching of the laser loop and the OEO loop, the final oscillation mode is more stable. By comparing the performance of the COEO-based, single-loop and dual-loop OEO-based sensors, the highest sensitivity of 41.1 Hz/(uMol/L) is obtained by the COEO-based sensor. Since the positive feedback of two loops, the single mode oscillation can be implemented without additional devices.

Switchable and tunable dual-wavelength passively mode-locked fiber laser

We demonstrate a switchable and tunable dual-wavelength passively mode-locked fiber laser in a compact linear cavity. Two cascaded polarization-maintaining fiber Bragg gratings (PM-FBGs) are used as wavelength-selective components, and a semiconductor saturable absorber mirror (SESAM) is used as a mode-locked component. Four kinds of switchable single-wavelength and two kinds of switchable dual-wavelength mode-locked operations are achieved in 1.0-μm band under lower pump power condition. Through temperature control, we obtain the tunable single-wavelength and dual-wavelength mode-locked operations, and the tunable wavelength range is about 0.5 nm when increase the temperature from 25 °C to 80 °C.

Structured plasmonic beam: in-plane manipulation of light at the nanoscale

The brief review on recent approaches on the formation of a new class of subwavelength scale localized structured surface plasmon polaritons (SPP) beams is discussed. For the Janus-like particle (including the geometrically symmetric particles with different dielectrics) the morphology of the field localization area and its properties depends on the particle shape and material. Plasmonic hook (PH) beam does not propagate along straight line but instead follow curved self-bending trajectory. Wavefront analysis behind of such symmetric and asymmetric mesoscale rectangle structure reveals that the unequal phase of the transmitted plane wave results in the irregularly concave deformation of the wavefront inside the dielectric which later leads to creation of the PH. Such dielectric structures placed on metal film enable the realization of new ultracompact wavelength-selective and wavelength-scaled in-plane nanophotonic components. SPP have potential to overcome the constrains on the speed of modern digital integrated devices limitation due to the metallic interconnects and increase the operating speed of future digital circuits.

Planck Spectroscopy (Laser Photonics Rev. 15(10)/2021)

Planck Spectroscopy Existing spectrometers rely on wavelength-selective optical components such as gratings or prisms. As featured on the cover, a new spectroscopic technique–Planck spectroscopy–that does not require any wavelength-selective optical components is demonstrated in article number 2100121 by Mikhail A. Kats and co-workers. The technique relies on the fundamental relationship that relates temperature to the spectrum of blackbody radiation and can be implemented using only a heater, photodetector, and computational algorithm.[Image credit: X. Zou]

Highly Stable and Precise Demodulation of an FBG-Based Optical Current Sensor Using a Dual-Loop Optoelectronic Oscillator

Electrical current monitoring plays an important role in power transmission system, electric instruments, etc. The stability of the monitoring system is highly demanded. In this paper, a new interrogation scheme for a fiber Bragg grating (FBG) current sensor based on a dual-loop optoelectronic oscillator (OEO) with high stability, high precision and simple structure is proposed and experimentally demonstrated. The wavelength shift of the FBG, which is bonded on a magnetostrictive alloy-strip, is converted into the frequency shift of the microwave signal through the OEO system utilizing the wavelength to frequency mapping mechanism. Different from previous single-loop OEO schemes, a length of ∼1 km single mode fiber is used to form the second loop in the OEO-cavity, which can enhance the mode-selection ability and reduce the total gain requirement of the system. In addition, a fiber-ring-laser (FRL) cavity is adopted by integrating the sensing FBG-head as the wavelength-selective component to improve the quality of the optical carrier signal. The measured side-mode suppression ratio (SMSR) is up to 62.59 dB and the free spectral range (FSR) is five times larger than the single-loop structure, resulting in highly-enhanced stability and so the precision. Most importantly, the frequency fluctuation is as low as 0.277 ppm, which is the minimum to the best of our knowledge. Compensating methods for the influence of the temperature and the hysteresis are also discussed. The proposed scheme provides a feasible solution to promoting the development of OEO-based interrogation technology and its commercial applications.

Sensor interrogation technique with multi‐wavelength laser based microwave photonic filter

AbstractIn this article, we have proposed and demonstrated a sensing interrogation scheme of microwave photonic filter (MPF) based on multi‐wavelength fiber laser (MWFL). A Mach‐Zehnder interferometer (FMZI) acts as the wavelength selective component in the laser cavity as well as the sensing element. An erbium doped fiber amplifier (EDFA) and a semiconductor optical amplifier (SOA) are employed as hybrid gain medium to suppress the homogeneous broadening of erbium doped fiber. The MWFL is employed as the optical source to implement the MPF together with a dispersive medium. The free spectrum range of interference pattern of the FMZI changes with the temperature variation, thus changing the central frequency of MPF's passbands. The sensitivities are −12.23 and 6.11 MHz/°C, respectively, when the sensing optical fiber with the length of 2.2 and 1.1 m are used.

Modeling of a quantum dot gain chip in an external cavity laser configuration

External cavity semiconductor lasers with strong optical feedback already exist using a gain chip medium. Owing to their ultrafast carrier dynamics, strong output power, and high temperature reliability, quantum dots as a gain medium are now envisioned as a promising solution to replace the current quantum well technology. This paper presents a semi-analytical rate equation model which is used to describe a quantum dot gain chip capable of lasing only with a free space external cavity laser. It investigates the evolution of the dynamical properties such as the turn-on delay and the damping rate. It also confirms the model’s validity through the relative intensity noise and the frequency noise with respect to both material and device parameters like the linewidth enhancement factor, the gain compression factor, or the cavity length. Overall, this numerical investigation provides initial building blocks for future fabrication research and development of high performance devices including filters or gratings as wavelength-selective components.

A Fiber Ring Cavity Laser Temperature Sensor Based on Polymer-Coated No-Core Fiber as Tunable Filter

A fiber ring cavity laser temperature sensor is presented and demonstrated. The sensor probe consists of a fiber Bragg grating (FBG) and a heterostructure based on polymer-coated no-core fiber (NCF), and this probe also functions as a wavelength-selective component in the fiber laser system. There are multimode interference and antiresonance effects in the NCF coated with high refractive index polymer. Embedding this sensing head into an Er-doped fiber ring cavity laser system is helpful to improve the spectral quality and the detection limit (DL). The passband peak position of the heterostructure filter and FBG filter varies with the temperature, which leads to the corresponding shift in the output laser wavelengths. Experimental investigation achieves a maximum sensitivity of −3.155 nm/°C in the temperature range from −4 °C to 47 °C, and the DL is calculated as 0.005 °C. It should be noted that there are several measurement intervals in this temperature range, which can be distinguished by the cascaded FBG to obtain the accurate temperature value. Moreover, the sensor with a smaller NCF diameter has a higher temperature sensitivity. The proposed sensor can meet the actual demands of mesoscale ocean phenomena and microregion temperature detection in seawater, and it provides references for improving the sensing capability of optical methods in ocean detection and other practical application.

Liquid level and temperature sensing by using dual-wavelength fiber laser based on multimode interferometer and FBG in parallel

Abstract The detection of liquid level and temperature based on a fiber ring cavity laser sensing configuration is presented and demonstrated experimentally. The sensing head contains a fiber Bragg grating (FBG) and a single-mode–cladding-less–single-mode multimode interferometer, which also functions as wavelength-selective components of the fiber laser. When the liquid level or temperature is applied on the sensing head, the pass-band peaks of both multimode interference (MMI) filter and FBG filter vary and the two output wavelengths of the laser shift correspondingly. In the experiment, the corresponding sensitivities of the liquid level with four different refractive indices (RI) in the deep range from 0 mm to 40 mm are obtained and the sensitivity enhances with the RI of the liquid being measured. The maximum sensitivity of interferometer is 106.3 pm/mm with the RI of 1.391. For the temperature measurement, a sensitivity of 10.3 pm/°C and 13.8 pm/°C are achieved with the temperature ranging from 0 °C to 90 °C corresponding to the two lasing wavelengths selective by the MMI filter and FBG, respectively. In addition, the average RI sensitivity of 155.77 pm/mm/RIU is also obtained in the RI range of 1.333–1.391.

Switchable dual-wavelength SLM narrow linewidth fiber laser based on nonlinear amplifying loop mirror

We demonstrate a stable switchable dual-wavelength single longitudinal mode (SLM) narrow linewidth ytterbium-doped fiber (YDF) laser using a nonlinear amplifying fiber loop mirror (NALM) at 1064nm. The NALM of intensity-dependent transmission acts as a saturable absorber filter and an amplitude equalizer to suppress mode competition and the fiber Bragg grating (FBG) pair is used as one wavelength selection component. By properly adjusting the polarization controllers (PCs), the switchable dual-wavelength SLM fiber laser can be operated steadily at room temperature. The optical signal-to-noise ratio (OSNR) is better than 50dB for both lasing wavelengths. Meanwhile, the linewidth of the fiber laser for each wavelength is approximate 17.07kHz and 18.64kHz with a 20dB linewidth, which means the laser linewidth is approximate 853Hz and 932Hz FWHM. Correspondingly, the measured relative intensity noise (RIN) is less than −120dB/Hz at frequencies over 5.0MHz.

Multi-Wavelength Thulium-Doped Fiber Laser Using a Fiber-Based Lyot Filter

A multi-wavelength thulium-doped fiber laser using a fiber-based Lyot filter is proposed in 2- $\mu \text{m}$ band for the first time. In the laser cavity, the fiber-based Lyot filter is used as the comblike wavelength selection component. By adjusting two polarization controllers, a stable multi-wavelength operation is obtained at room temperature, 17 output channels within 10-dB bandwidth from 1982 to 1998 nm are achieved. The flattened spectrum of multi-wavelength operation can obtained by using the 10% output coupling ratio. The different wavelength spacing of the fiber laser can be controlled by adjusting the polarization maintaining fiber lengths of the Lyot filters.

Flexible and re-configurable optical three-input XOR logic gate of phase-modulated signals with multicast functionality for potential application in optical physical-layer network coding.

Optical logic gate, especially exclusive-or (XOR) gate, plays important role in accomplishing photonic computing and various network functionalities in future optical networks. On the other hand, optical multicast is another indispensable functionality to efficiently deliver information in optical networks. In this paper, for the first time, we propose and experimentally demonstrate a flexible optical three-input XOR gate scheme for multiple input phase-modulated signals with a 1-to-2 multicast functionality for each XOR operation using four-wave mixing (FWM) effect in single piece of highly-nonlinear fiber (HNLF). Through FWM in HNLF, all of the possible XOR operations among input signals could be simultaneously realized by sharing a single piece of HNLF. By selecting the obtained XOR components using a followed wavelength selective component, the number of XOR gates and the participant light in XOR operations could be flexibly configured. The re-configurability of the proposed XOR gate and the function integration of the optical logic gate and multicast in single device offer the flexibility in network design and improve the network efficiency. We experimentally demonstrate flexible 3-input XOR gate for four 10-Gbaud binary phase-shift keying signals with a multicast scale of 2. Error-free operations for the obtained XOR results are achieved. Potential application of the integrated XOR and multicast function in network coding is also discussed.

Tunable and switchable fiber laser based on modal interference

A tunable and switchable erbium-doped fiber (EDF) laser based on modal interference has been proposed and experimentally demonstrated in this paper. Here a core-offset structure has been used to excite the cladding modes and a segment of polarization maintaining fiber inserted in a Sagnac loop interferometer has been used as wavelength selective component. By adjusting the statement of polarization controller (PC) and the bending of the core-offset structure, a tunable and switchable fiber laser with the signal-to-noise ratio (SNR) of more than 50 dB has been achieved in this paper.

Switchable and tunable dual-wavelength single-longitudinal-mode erbium-doped fiber laser with special subring-cavity and superimposed fiber Bragg gratings

A switchable and tunable dual-wavelength single-longitudinal-mode (SLM) erbium-doped fiber laser (EDFL) has been proposed and demonstrated. Two superimposed fiber Bragg gratings (SI-FBG) have been used as one original wavelength selection component. A special subring-cavity was employed to select the SLM. By properly adjusting a polarization controller, single- and dual-wavelength switchable operations with high wavelength and power stability were realized experimentally. Regardless of which work mode, the signal to noise ratio was higher than 60 dB and the polarization extinction ratio was higher than 20 dB. The wavelength-spacing was 9.96 nm, indicating that it can be used to generate continuous-wave terahertz waves. The linewidth of each lasing wavelength measured by the delayed self-heterodyne method was approximately 1.25 kHz and 1 kHz, respectively. By stretching the SI-FBG, the EDFL had a wavelength-tunable range of 5.96 nm in both the single- and dual-wavelength operations.

Asymmetric hybrid plasmonic waveguides with centimeter-scale propagation length under subwavelength confinement for photonic components.

An asymmetric hybrid plasmonic metal-wire waveguide is proposed by combining the advantages of symmetric and hybrid plasmonic modes. The idea of asymmetric structure eliminates the adverse effect of a substrate and enhances the optical performance of the waveguide. The guiding properties of the proposed waveguide are intensively investigated using the finite elements method. The results exhibit a quite long propagation length of 2.69 cm with subwavelength confinement. More importantly, an extremely large figure of merit of 139037 is achieved. Furthermore, the proposed waveguides can be used as directional couplers. They can achieve a coupling length of only 1.01 μm at S = 0.1 μm with negligible loss. A strong dependence of coupling length on the operating wavelength makes the proposed waveguide promising for realizing wavelength-selective components at telecommunication wavelengths.

1+1 Dedicated Optical-Layer Protection Strategy for Filterless Optical Networks

We propose a dedicated optical-layer protection strategy for filterless optical networks offering a 100% protection ratio by introducing a limited number of wavelength selective components at selected intermediate nodes. A comparison with conventional active photonic switching networks is presented. The results show that the proposed 1+1 protection for filterless networks exhibits a clear cost advantage at similar wavelength usage compared to active switching solutions.

Ultra-long-range symmetric plasmonic waveguide for high-density and compact photonic devices

This study reports a symmetric hybrid plasmonic waveguide consisting of a cylindrical metal nanowire surrounded by low-index SiO₂ and high-index Si covered with SiO₂. The symmetric circumambience relative to the metal nanowire significantly facilitates the present design to minimize the energy attenuation resulting from Ohmic losses while retaining highly confined modes guided in the low-index nanoscale gaps between the metal nanowire and the high-index Si. The geometric dependence of the mode characteristics on the proposed structure is analyzed in detail, showing long propagation lengths beyond 10 mm with normalized mode areas on the order of 10⁻². In addition to enabling the building of long-range plasmonic circuit interconnects, the compactness and high-density integration of the proposed structure are examined by analyzing crosstalk in a directional coupler composed of two such waveguides and bending losses for a 90° bend. A relatively short coupling length of 1.16 μm is obtained at a center-to-center separation of 0.26 μm between adjacent waveguides. Increasing the separation to 1.65 μm could completely prevent coupling between waveguides. Power transmission exceeds 80% in the case of a 90° bend with small radius of curvature of 0.5 μm. Moreover, the dependence of spectral response on coupling length and the transmission of a 90° bend, ranging from telecom wavelengths of 1.40 to 1.65 μm, are investigated. Over a wide wavelength range, a strong coupling length dependence on wavelength and a high transmission for a 90° bend also make the proposed plasmonic waveguide promising for the realization of wavelength-selective components.

A widely tunable, dual-wavelength fiber laser incorporating two polymer waveguide Bragg gratings

We present a continuously tunable dual-wavelength fiber laser based on polymer waveguide Bragg grating (PWBG) filters. The PWBG filters are used as wavelength selective components in the laser cavity. The 3 dB linewidth of the lasing wavelength is measured to be 0.02–0.04 nm over the whole wavelength tuning range. This range is 18.9 nm, from 1546.6 to 1527.7 nm. A linear response of the peak wavelength to the applied electrical power is achieved. The tuning efficiency of the single wavelength is −0.19 nm mW−1. The wavelength spacing for the dual-wavelength fiber laser is tuned from 1.2 to 18.9 nm. The side-mode suppression ratio achieved is more than 35 dB over the whole tuning range. Stability of the dual-wavelength laser is accomplished by careful adjustment of the polarization states of the dual wavelengths.

Stable dual-wavelength single-longitudinal-mode ring erbium-doped fiber laser for optical generation of microwave frequency

We demonstrate a simple dual-wavelength ring erbium-doped fiber laser operating in single-longitudinal-mode (SLM) at room temperature. A pair of reflection type short-period fiber Bragg gratings (FBGs), which have two different center wavelengths of 1545.072 and 1545.284 nm, are used as the wavelength-selective component of the laser. A segment of unpumped polarization maintaining erbium-doped fiber (PM-EDF) is acted as a narrow multiband filter. By turning the polarization controller (PC) to enhance the polarization hole burning (PHB), the single-wavelength and dual-wavelength laser oscillations are observed at 1545.072 and 1545.284 nm. The output power variation is less than 0.6 dB for both wavelengths over a five-minute period and the optical signal to noise ratio (OSNR) is greater than 50 dB. By beating the dual-wavelengths at a photodetector (PD), a microwave signal at 26.44 GHz is demonstrated.