Improved Range Tunability of DFB Lasers Based on REC Technique Under Injection Current

A 16-channel electroabsorption modulated tunable multi-wavelength DFB laser array is proposed and experimentally demonstrated. The sixteen DFB lasers, each with a wavelength spacing of 100 GHz, are arranged in a 4 × 4 matrix. The wavelengths are designed using an interleaving scheme to reduce grating crosstalk. The grating is designed and fabricated using the reconstruction equivalent chirp (REC) technique to simplify the grating fabrication and ensure precise wavelength control. The electroabsorption modulator and the tunable multi-wavelength laser array share the same active layer to reduce fabrication complexity and costs. Wavelength tuning is achieved by selecting the active laser without altering the thermoelectric cooler (TEC). Consequently, 16 channels with 100 GHz spacing are obtained, each operating in good single-mode properties with SMSRs of above 45 dB. The average wavelength spacing is 106.1 GHz, and only 6.1 GHz deviated from the design. The semiconductor optical amplifier (SOA) is integrated to compensate for the frequency chirp and amplify the output power, thus enabling long-distance transmission. The output power is amplified to over 18 mW with a 150 mA current injected into the SOA. The 3-dB bandwidth of the EAM exceeds 20 GHz, producing clear 25 Gb/s back-to-back eye diagrams with mask margins over 40% for the 16 channels. With the assistance of the chirp compensation by the SOA, the eye diagrams of the 16 channels remain clear after 10 km of transmission. Due to the superior performance, the proposed device is promising for use in DWDM systems, particularly in applications requiring fast channel switching, such as optical packet switching and NG-PON2 technology.

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.

Summary form only given. Birefringent filters are routinely used as a wavelength tuning element in bulk optics, broadly tunable lasers such Ti:Sapphire [1] and dye lasers. A detailed description of birefringent filter operation can be found in ref. [2]. In this paper, we report the design, fabrication and characterisation of an integrated electro-optically tunable birefringent filter for wavelength and polarisation tuning of quantum cascade lasers (QCLs) [3].Our generic design for an integrated tunable birefringent filter (ITBF) for QCLs is shown in Fig. 1(a). It consists of 2 quarter waveplates with a differential phase shift (DPS) section between them. The integrated equivalents of waveplates are polarization mode convertors (PMC) [4] that converts the TM (Transverse Magnetic) polarised light from the gain section into circularly polarised light. In a QCL there is only gain for TM modes because of the intersubband transition selection rules. The DPS section adjusts the relative phase of the TM and TE (Transverse Electric) components of the circularly polarized light from the first PMC (PMC1 in figure 1(a)); this is because the birefringence of DPS section can be adjusted by injection current. The relative phase of the TE and TM components at the input into the second PMC (PMC 2 in figure 1(a)) determines the output polarization. In a QCL, only TM light will experience gain and the wavelengths that are rotated back to TM polarization are determined by the current in the DPS section. Thus we have a QCL that has its operating wavelength selected by an electro-optic tunable birefringent filter. For wavelength tuning the gain section was operated pulsed (100 ns pulse width at 60 kHz repetition rate) above threshold, at a current density of 6.8 kA/cm, and wavelength tuning was recorded (shown in Fig. 1(b)) for various values of DC injection current density into the DPS up to 24nm at 0.41kA/cm2. In our polarization control experiments at 0 kA/cm2 a maximum throughput polarisation angle of 37O was recorded and this angle increases up to 82O with an applied DC current of 0.97 kA/cm2 into the DPS and no further change in polarization angle recorded above 0.97 kA/cm2 current density (shown in Fig. 1(c)).In summary we have presented results on a QCL that includes an integrated birefringent filter. The results show that the output wavelength and polarisation can be electro-optically tuned by injecting a DC current into a differential phase shift section.

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.

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.

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.

TOPTICA's continuously tunable laser, the CTL, enables mode‐hop‐free wavelength tuning up to 120 nm with narrow linewidth and highest accuracy. With applications in device characterization, quantum and materials analysis, it is ideal for any application requiring high precision mode-hop free laser operation over a wide tuning range. In this demo, Dr. Rudolf Neuhaus demonstrates how to operate the laser with the fully digital, low noise and drift DLC pro controller using intuitive touch screen controls. To illustrate the convenient features of the laser and DLC pro controller, the system is connected to a spectroscopy cell and the transmission spectra is measured by a photodiode and recorded by the DLC pro with the ability to review the data live and adjust operating parameters accordingly, including the ability to lock the laser to a specific laser line. For more information about the CTL, contact us at sales@toptica-usa.com.

A tunable twin-guide laser diode (TTGLD) is one of the most attractive laser diodes, in terms of smooth wavelength tunability with wide tuning range.1 The major problem with TTGLD’s is the simultaneous loss increase in the tuning layer associated with tuning current increase, which results in limited wavelength tunability. In this paper we demonstrate a novel TTGLD with a carrier-controlled tuning layer (InGaAsP SCH-MQW structure), where the refractive-index change and the loss increase are separately controlled. The increase in optical absorption loss associated with refractive-index change was suppressed by a factor of 3 compared with that for bulk-tuning-layer devices.

The tuning characteristics of a novel tunable semiconductor laser structure are presented. Discontinuous tuning ranges of up to 29.6 nm and quasi-continuous tuning ranges up to 14.7 nm have been measured in 1550 nm wavelength three section sampled grating distributed Bragg reflector lasers (DBR). The three section lasers presented allow wide range tuning by adjustment of the round trip phase condition combined with a sampled grating DBR periodic reflectivity and give the possibility of very fast wavelength mode switching.

The wavelength tuning and intensity modulation characteristics are presented for three types of twin-guide (TG) lasers entirely fabricated by metalorganic vapour phase epitaxy (MOVPE). A wide continuous tuning range of 5.3 nm is obtained for the tunable twin-guide (TTG) laser. The TTG lasers, however, have the drawbacks of output power reduction and spectral linewidth broadening during tuning. A new type of tunable laser, the complementary twin-active-guide (CTAG) laser, is proposed, and its tuning characteristics are presented for the first time. A wide continuous tuning range over 4 nm is obtained, although the thermal effect is more dominant than carrier effects. The CTAG structure enables suppression of the spectral linewidth broadening induced by the injected carrier recombination shot noise (IRSN) during tuning. The characteristics of the TG lasers modulated by reverse bias are presented, and the possibility of using these TG lasers for wavelength tuning is studied.

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.

An overview is given about recent results on static and dynamic properties of InP-based quantum dot lasers. High temperature stability in directly modulated lasers (T0 > 100 K, T1 > 500 K, up to 35 GBit/s) and narrow linewidth (< 150 kHz) with wide wavelength tuning range (C+ band) in an integrated QD DFB laser chip are obtained.

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.

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTOptical systems unravel smog chemistryJames N. Pitts Jr., Barbara J. Finlayson-Pitts, and Arthur M. WinerCite this: Environ. Sci. Technol. 1977, 11, 6, 568–573Publication Date (Print):June 1, 1977Publication History Published online1 May 2002Published inissue 1 June 1977https://pubs.acs.org/doi/10.1021/es60129a014https://doi.org/10.1021/es60129a014research-articleACS PublicationsRequest reuse permissionsArticle Views90Altmetric-Citations32LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access optionsGet e-Alertsclose Get e-Alerts