Full C-Band Tunable DFB Laser Array Copackaged With InP Mach–Zehnder Modulator for DWDM Optical Communication Systems

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.

The future of optical interconnection needs for high optical coupling efficiency for high density multi-layer printed wiring board (PWB). Hence, a self-written waveguide (SWW) optical pin is implemented between surface device and multi-layer channel as optical coupling for reaching high coupling efficiency. A comparatively studies of three configurations of coupling methods was carried out by ray-tracing simulation. The correlation between optical coupling efficiency and mirror angle was analyzed as well as the relationship between optical coupling efficiency and photodiode (PD) positional. A maximum value of optical coupling efficiency with optical pin is obtained for both correlations. The 1 dB down-tolerance width of the correlation between optical coupling efficiency and the mirror angle for vertical pin (case 1) is larger compared to case 2 and case 3 (without vertical pin). For the relationship between optical coupling efficiency and PD positional error, the 1 dB down-tolerance widths for case 1, case 2 and case 3 were ±13μm, ±19μm and ±20μm, respectively. From this result, it is found that vertical pin is well-suited to satisfy both coupling efficiency and tolerance for shifting mirror angle and PD positional error.

A tunable fiber ring laser based on an in-line two-taper Mach-Zehnder interferometer (MZI) filter was realized, and the effect of beam waists of the tapers on performance of the laser was investigated with different beam waists of 70 μm, 49 μm, and 33 μm. Experimental results show that the tunable laser with MZI length of 1 m and beam waist of 49 μm can cover 16.1 nm with tuning steps of 0.07-0.5 nm, a bandwidth of 10 pm, and a side mode suppression ratio (SMSR) of 40-50 dB. Tuning range is not only determined by the number of the cladding modes but is also affected by the filter loss. Tuning step is determined by the differences of the effective refractive indexes between the cladding modes and the core mode. SMSR is determined by the balance between the extinction ratio of the filter and the cavity loss of the laser due to MZI filter.

To realize a high-speed high-reliability wavelength switching at future WDM networks, we proposed the injection current/temperature cooperative control method of the tunable-distributed-feedback (DFB) laser array (TLA) for avoiding a large injection current, which is the primary cause of laser degradation. We successfully demonstrated a full-C-band wavelength switching within 124 ms by rapid increase of the injection current and following gradual decrease of the injection current to avoid laser aging. Compared to the conventional control method, the meantime to failure of the TLA in the proposed method is estimated to be extended by 44 times.

We studied a high-speed high-reliability wavelength switching at 400-GHz width, which is the maximum tuning range of a single DFB laser in the tunable DFB laser array (TLA). By improving the accuracy of current/temperature cooperative feedback control, we achieved a high-speed wavelength switching time of 130 ms as well as a low injection current of 52 mA.

Two wavelength-spacing continuously tunable multi-wavelength fiber lasers based on four-wave-mixing effect, one with a dispersion-shifted fiber and the Mach-Zehnder interferometer, the other with a highly nonlinear fiber and the two tunable lasers, are proposed.

Quasi-Vertical tapers are designed to enable high coupling efficiency from a conventional single mode fiber into a single mode polymer rib waveguide. A triangular region fabricated under the single mode waveguide is adopted to adiabatically transform the fiber mode into the polymer rib waveguide mode. This structure works as an optical mode transformer. Because the trenches are deeper at the facets than at the active regions of the waveguide, the waveguide mode size in vertical direction becomes larger at the facets and can better match the input and output fiber mode. A coupling efficiency of 82.95% is achievable with a tip width of 1 μm .

We demonstrate a fast Quasi-Continuous frequency scanning semiconductor laser source for optical fiber sensor interrogation systems. The tunable laser covers a wavelength range of 32nm in C-band with tuning resolution of 8pm. The scanning time over the complete wavelength range in C band is less than 1ms while the switching time from one wavelength point to another point can be less than 100ns. A fast current driver controlled using FPGAs have been employed to drive a DSDBR laser for the realization of the fast tunable laser module. Experimental results have verified its possible application in optical sensor interrogation systems.

Effects of filter bandwidth and driving voltage on optical duobinary transmission systems

A 12-channel 100-GHz-spacing thermally tunable multi-wavelength DFB laser array is demonstrated based on reconstruction-equivalent-chirp technique with good single-longitudinal-mode property (SMSR > 50 dB) and small temperature tuning range (15.5 °C).

One of the key mandates of modern optoelectronic research is the development of compact photonic integrated circuits, capable of performing many diverse functions for the generation, manipulation, and detection of light, all on a single chip. A key practical requirement for such circuits is the development of optical devices for the localization and processing of light within extremely small dimensions. In recent years, planar microring and microdisk resonators, in which light is confined by total internal reflection, have emerged as versatile photonic elements for filling this role. The high quality factors and long photon storage times associated with the whispering-gallery modes supported by these microcavities result in several technologically useful characteristics, including narrow-band filter response, and large resonant enhancement of the circulating electric field. These properties have been exploited in numerous passive and active device applications, including optical add/drop multiplexers, all-optical switches, and tunable lasers. This thesis describes the study of several unique ring-based optical microcavity geometries based upon the indium gallium arsenide phosphide/indium phosphide alloy semiconductor material system, undertaken in an effort to explore new optoelectronic architectures for confining and manipulating light. The first portion of this work involves the analysis and demonstration of a new microcavity geometry, in which cylindrical Bragg reflection is used for radial optical confinement, as an alternative to total internal reflection. In this class of structures, collectively known as annular Bragg resonators, light can be guided within a ring or pillar defect layer surrounded by cylindrical Bragg mirrors. Several microcavities based upon this configuration are designed and fabricated using a thin InGaAsP quantum well membrane. Using pulsed optical excitation, the characteristics of these structures as low threshold vertically emitting lasers is explored. Second, a total internal reflection-based coupled waveguide-resonator geometry, having applications to low power optical switching and modulation, is analyzed. This geometry makes use of the hybrid integration of a Mach-Zehnder interferometer with a racetrack resonator. Switching takes place using the Mach-Zehnder to control the coupling parameters in the vicinity of the critical coupling condition. Characterization of the static and dynamic output response of a thermooptically actuated InGaAsP-InP hybrid switch device demonstrates good ON-OFF switching contrast, microsecond response time, and reduced switching power in comparison with a conventional Mach-Zehnder configuration. Finally, this work concludes by examining both the annular Bragg resonator and hybrid switch geometries in application to chemical and biological sensing. Both microcavity devices are shown to possess unique characteristics making them ideal for sensitive monitoring of small changes in the refractive index of a chemical or biological analyte.

A compact tunable laser module integrating a newly developed DBR/Ring laser and an extremely-high- Δ PLC wavelength locker is demonstrated with narrow spectral linewidth of <100 kHz across the full C-band.

The Far-Infrared Fourier transform spectrometer instrument SAFARI-SPICA which will operate with cooled optics in a low-background space environment requires ultra-sensitive detector arrays with high optical coupling efficiencies over extremely wide bandwidths. In earlier papers we described the design, fabrication and performance of ultra-low-noise Transition Edge Sensors (TESs) operated close to 100mk having dark Noise Equivalent Powers (NEPs) of order 4 × 10−19W/√Hz close to the phonon noise limit and an improvement of two orders of magnitude over TESs for ground-based applications. Here we describe the design, fabrication and testing of 388-element arrays of MoAu TESs integrated with far-infrared absorbers and optical coupling structures in a geometry appropriate for the SAFARI L-band (110 − 210 μm). The measured performance shows intrinsic response time τ ~ 11ms and saturation powers of order 10 fW, and a dark noise equivalent powers of order 7 × 10−19W/√Hz. The 100 × 100μm2 MoAu TESs have transition temperatures of order 110mK and are coupled to 320×320μm2 thin-film β-phase Ta absorbers to provide impedance matching to the incoming fields. We describe results of dark tests (i.e without optical power) to determine intrinsic pixel characteristics and their uniformity, and measurements of the optical performance of representative pixels operated with flat back-shorts coupled to pyramidal horn arrays. The measured and modeled optical efficiency is dominated by the 95Ω sheet resistance of the Ta absorbers, indicating a clear route to achieve the required performance in these ultra-sensitive detectors.

10-Gbit/s optical duobinary transmission over a 200-km single-mode fiber is demonstrated using a lossless InP n-p-i-n Mach-Zehnder modulator monolithically integrated with a semiconductor optical amplifier. The device gain exceeds 8 dB and the static extinction ratio is over 26 dB for a wavelength of 1550 nm. An error free operation was achieved with a power penalty of less than 5 dB at a low driving voltage of 2.8 Vpp for push-pull operation.

We have developed InP-based Mach-Zehnder modulators suitable for advanced modulation formats using a novel waveguide structure. We confirmed 40-Gbit/s NRZ signal generation and a 220-km 10 Gbit/s optical duobinary transmission. We also demonstrated a DQPSK modulator operating at 80 Gbit/s.