Wavelength tuning in three section sampled gratingDBR lasers

Intensity modulation characteristics of a 1.5- mu m butt-jointed DBR (distributed-Bragg-reflector) laser with wavelength tuning were studied. A 3-dB modulation bandwidth of 9 GHz and a high relaxation oscillation frequency of more than 10 GHz were obtained for the DBR laser. These characteristics were not affected by changing the lasing wavelength. The chirping width of the DBR laser is lower than that of the distributed feedback (DFB) laser. A clear eye opening and low chirping characteristics were obtained under 5-Gb/s nonreturn to zero (NRZ) pseudorandom modulation with a sufficient extinction ratio.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

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.

Wavelength tunable and directly modulated distributed Bragg reflector (DBR) lasers with butt-joint technology are designed, fabricated and characterized. The DBR laser consists of a gain section and a DBR section. To increase the electrical isolation between the gain section and the DBR section, parts of a p-doped material in the isolation region are etched off selectively. Over 2 kΩ isolation resistance is realized ultimately without the need of ion implantation, which simplifies the fabrication process. The laser exhibits high speed modulation with a large tunable range. The 3 dB direct modulation bandwidth of the device is over 8 GHz in a 12 nm tunable range. This widely tunable DBR laser with the simple structure is promising as a colorless light source for the next-generation time and wavelength division multiplexed passive optical network (TWDM-PON) systems.

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

Chip-scale lasers with a wide tunable range and a narrow linewidth have rich applications in optical communications, sensing, and light detection and ranging systems. External cavity lasers (ECLs) have the advantage of a wide tuning range and a narrow linewidth compared with their counterparts such as distributed feedback lasers and distributed Bragg reflector lasers because the passive filter separated from the gain section can be widely tuned and the low-loss external cavity extends the photon lifetime. However, so far, the tuning range achieved by the chip-scale ECLs is in the range of 80–120 nm, smaller than that of the bulk free-space ECL (typically &amp;gt;160 nm). The bottleneck in reaching an ultrabroad tuning range for chip-scale ECLs lies in the unsuppressed side modes of the external cavity. Here, we demonstrate a hybrid-integrated ECL consisting of a broadband III–V reflective semiconductor optical amplifier and a low-loss Si3N4 wavelength-selective reflector. A record 172-nm lasing wavelength tuning range together with a more than 40 dB side-mode suppression ratio is achieved beyond the free spectral range of the Vernier ring filter due to the enhanced lasing mode selection from a tunable Sagnac loop reflector. The Si3N4 platform enables a low-loss external cavity, facilitating laser linewidth reduction below 4 kHz over the full tuning range. The on-chip output power reaches 26.7 mW at a wavelength of 1550 nm.

Wavelength tunable electro-absorption modulated distributed Bragg reflector lasers (TEMLs) are promising light source in dense wavelength division multiplexing (DWDM) optical fiber communication system due to high modulation speed, small chirp, low drive voltage, compactness and fast wavelength tuning ability. Thus, increased the transmission capacity, the functionality and the flexibility are provided. Materials with bandgap difference as large as 250nm have been integrated on the same wafer by a combined technique of selective area growth (SAG) and quantum well intermixing (QWI), which supplies a flexible and controllable platform for the need of photonic integrated circuits (PIC). A TEML has been fabricated by this technique for the first time. The component has superior characteristics as following: threshold current of 37mA, output power of 3.5mW at 100mA injection and 0V modulator bias voltage, extinction ratio of more than 20 dB with modulator reverse voltage from 0V to 2V when coupled into a single mode fiber, and wavelength tuning range of 4.4nm covering 6 100-GHz WDM channels. A clearly open eye diagram is observed when the integrated EAM is driven with a 10-Gb/s electrical NRZ signal. A good transmission characteristic is exhibited with power penalties less than 2.2 dB at a bit error ratio (BER) of 10^-10 after 44.4 km standard fiber transmission.

Multiple wavelength sources are of interest in optical communications, optical data processing, spectroscopy, and RF and THz generation by optical heterodyning. Our results demonstrate a tunable dual-wavelength source consisting of two surface-etched distributed Bragg reflector (DBR) lasers with outputs combined by a y-branch coupler, suitable for optical heterodyning. The integrated device presented here has the distinct advantages of a wide range of tunability, extending into the terahertz frequency range, as well as a compact design, requiring the use of no external components. While y-branch DBR lasers at 850nm have been previously explored, the devices reported here have a simplified fabrication process, optimized epitaxial structure, and surface etched gratings, which contribute to significant improvement in output power and wavelength tunability.

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.

We demonstrate a widely tunable distributed Bragg reflector (DBR) laser operating at 1.8-µm, in which the DBR section was butt-jointed InGaAsP (λ = 1.45 μm) material. Through current and temperature tuning, a widely tuning range of over 11 nm with a side mode suppression ratio (SMSR) higher than 30 dB is obtained. Utilizing this DBR laser, the water and methane detection experiment has been successfully implemented, which illustrates the potential capacity of such DBR laser as the light source used for multispecies gas sensing. The work also illustrates that the butt-joint active-passive integration technology developed for the InGaAsP quantum-wells (QWs) can be successfully applied in the InGaAs QWs.

Tunable laser diodes are now widely used in dense wavelength division multiplexing (DWDM) optical fiber networks. A wide tunability range and good frequency stability are generally required, without mode hopping. Special applications require fast frequency measurement. Unfortunately, commercially available classical spectral measurement systems are much too slow for that purpose. In this paper, we present a new and low-cost system dedicated to fast spectral measurements based on a Michelson interferometer. The free spectral range (FSR) of the interferometer must be carefully optimized. We have designed optimized and tested an experimental system that can quickly analyze with good accuracy the tunability range of tunable distributed Bragg reflector (DBR) laser diodes, and their possible mode hopping. Our set-up can also be used for other spectral measurements (linewidth, chirp, Henry's alpha enhancement factor, spectral and power monitoring). After theoretical analysis of our experimental set-up, we finally present the fast spectral measurements results obtained with a typical 1550 nm two sections DBR QW (quantum well) laser diode. Our measurements have been obtained within less than 500 ps, which is much faster than limits induced by switching thermal effects in laser diodes, and that speed could still be increased.

A frequency-tuning negative-conductance (-G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> ) boosted structure and applications for a voltage-controlled oscillator (VCO) is presented in this paper. Analog tuning varactors connected to a -G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> boosted structure is proposed to significantly alleviate the limitation of the tuning range for the -G <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">m</sub> boosted structure, resulting in a low-voltage low-power wide-tuning-range VCO. Based on the proposed architecture, the fabricated 0.18-μm CMOS VCO exhibits a measured 49.8% tuning range. Operating at 0.65 V low supply voltage, the VCO core consumes 2.37-mW dc power. At this bias condition, the measured average value of phase noise for all frequency ranges is -115.1 dBc/Hz at 1-MHz offset from the carriers. Relative to recently published wide-tuning-range CMOS VCOs, the proposed VCO simultaneously achieves low supply voltage, low dc power dissipation, low phase noise, and a wide tuning range, leading to a good figure-of-merit (FOM) and FOM including the tuning range. Furthermore, formulas of analysis for the proposed frequency-tuning -Gm boosted structure and wide VCO tuning range are presented, and the mechanisms are validated by experiments.

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.

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.

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 report 20 Gb/s transmission of four-level pulse amplitude modulation (PAM) signal using a directly modulated tunable distributed Bragg reflector (DBR) laser. Transmission distance over 20 km was achieved without using optical amplifiers and optical dispersion compensation modules. A wavelength tuning range of 11.5 nm and a 3 dB bandwidth greater than 10 GHz over the entire wavelength tuning range were obtained.