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We report a tunable distributed Bragg reflector-laser diode (DBR-LD) integrated with an electro-absorption-modulator (EAM) at an operating wavelength of 1.3 µm. This LD consists of gain, phase control (PC), DBR, and EAM sections, realized by using a butt-coupling technique in monolithically integrating the multiple quantum wells (MQWs) with the passive core and by applying an etched-mesa buried hetero-structure (EMBH) to the resonance cavity (i.e., gain to DBR section) and a deep-ridge type to the EAM section in fabricating the waveguide structure. Wavelength tuning of the LD is achieved by both applying a voltage to the heater metal of DBR section (coarse tuning) and injecting a current to the ohmic metal of PC section (fine tuning). From the work, the fabricated chips show a threshold current of about 13 mA, a side mode suppression ratio (SMSR) of more than 35 dB, and a tuning range of 15 nm within a heater voltage of 2 V. Dynamic tests for the EAM-integrated LD show the 3 dB bandwidth of more than 20 GHz and clear 25 Gb/s eye openings with a dynamic extinction ratio (DER) of over 7 dB for 16 channels spaced at the wavelength interval of 0.55 nm. Based on these results, we conclude that the EAM-integrated DBR-LD is capable of providing 16 channel operation at a data rate of 25 Gb/s and can be used as an effective light source for WDM-based mobile front-haul networks.

We present a 10-Gb/s 1.59- $\mu \text{m}$ directly modulated laser (DML) capable of a 20-km transmission in a standard single-mode fiber without the use of any other compensation techniques. For the fabricated distributed feedback laser diode chips, the static, dynamic, and transmission properties were tested. During these tests, it appears that the signal quality was improved after a certain transmission distance. To examine the change in signal shape during the transmission, a time-resolved back-to-back signal was measured and its transmission properties simulated. The simulated results of a time-resolved signal show good agreement with those obtained from a transmission test. As a result, it was confirmed that a 10-Gb/s DML signal (with an extinction ratio of 4 to 5 dB) can be transmitted at up to 20 km with a power penalty of less than 1 dB.

We have developed the sampled-grating distributed Bragg reflector (SG-DBR) tunable lasers which consist of gain sections, a phase control section, front/rear mirrors, and an amplifier. Various structures were implemented for iTLA application and coherent communication. As for the integration structure in these types of lasers, the butt-coupling method was used, and the waveguide structures as well as fabrication methods were optimized for high coupling efficiency.

We present a multi-channel $\lambda $ /4-shifted distributed feedback laser diode array (DFB-LDA) for the low-cost application of wavelength division multiplexing-based datacenter networks. The gain spectrum and lasing wavelength of each channel are controlled by utilizing selective area growth and E-beam lithography techniques, respectively. To reduce the power consumption and improve the channel uniformity of the proposed array, a planar-buried hetero-structure (PBH) is introduced and the region containing the active region and the current blocking structures are etched in a mesa form (i.e., an etched mesa PBH). From this study, it was found that an 8-channel 300- $\mu \text{m}$ -long anti-reflection (AR) $\lambda $ /4-shifted DFB-LDA has a threshold current of 10 mA, ±1.5 mA, and a side mode suppression ratio of over 50 dB for all channels. A transmission test for this LDA showed a clear eye opening with a dynamic ratio of over 4.5 dB at 10 Gb/s, and a power penalty of less than 2 dB after a 2-km transmission.

We report a 1.3-µm and 10-Gbps tunable distributed Bragg reflector laser diode (DBR-LD) for the low-cost application of a wavelength division multiplex based mobile front-haul network. The device consists of gain, phase control, and DBR sections, implemented using a butt-coupling method through a monolithic integration and through the introduction of an etched mesa planar buried hetero-structure in a waveguide structure. From the work, a 560-µm long DBR-LD with a 220-µm long micro-heater DBR section has a threshold current of 10 mA ± 1 mA and a tuning range of more than 15 nm within a heater injection current of ∼100 mA. Spectral and dynamic tests for this LD show 16 channels spaced a wavelength grid of 0.8 nm with a side mode suppression ratio of greater 40 dB and clear eye openings with a dynamic extinction ratio of over 5.4 dB at an operating current of 60 mA.

We report a new design for a superluminescent diode (SLD) that can provide a nearly circular output beam shape and a high output power in a tunable external cavity laser (T-ECL). The proposed SLD consists of an active region and a spot size converter (SSC) region. The active region is realized using a planar buried hetero structure for low electrical and optical leakages and the SSC region is realized using a buried deep ridge waveguide (BD-RWG) for narrow far-field patterns. In particular, we investigate the effects of the structural parameters in the SSC region on the output chip power and field patterns. In our structure, as the width of the passive waveguide core layer decreases, both the lateral and vertical far-field patterns tend to converge at ~ 13° under an etching depth of BD-RWG of ≥ 9 μm. The measured data agree well with the simulated results. Using this design, we can increase the output power of T-ECL from 3.7 to 7.9 mW at an injection current of 60 mA.

Aroma volatile changes of netted muskmelons (Cucumis melo L. cv. Earl’s Together) during growth, maturation and ripening stages were investigated in relation to ethylene and respiration production. While melons exhibited a small respiration peak 48 days after pollination (DAP), ethylene production was negligible throughout the developmental stages. Thus, this cultivar should be classified as a non-climacteric type. Using headspace SPME, 27 aroma volatile compounds were identified (10 esters, 8 aldehydes, 7 alcohols, 1 sulfur compound and 1 terpene). Among them, (Z)-6-nonenal, nonanal, (E,Z)-2,6-nonadienal and (E)-2-nonenal were largely and mainly found in immature fruits, and they were still major to the later stages. However, from 45 DAP many esters appeared and their percentages increased as fruits were ripening. Two major ester formation genes, alcohol dehydrogenase and alcohol acyl transferase transcriptions were up-regulated to some extent. For that reason, it may be possible to form ester compounds in non-climacteric melons through ethylene independent pathways.

We report a tunable external cavity laser (T-ECL) using a superluminescent diode (SLD) and a polymer Bragg reflector with 0.8-nm mode spacing 25 channels operating in the direct modulation of 2.5 Gb/s for a low-cost source of a wavelength division multiplexed passive optical network (WDM-PON) system. The maximum output power is 12.2 mW and the slope efficiency of the T-ECL is about 0.12-0.17 mW/mA in the tuning range of 20 nm at the SLD current of 50 mA and at the temperature of 25°C. The T-ECL successfully operated in the direct modulation for 2.5-Gb/s transmission through 20-km standard single-mode fiber. The power penalty of the T-ECL is less than 0.8 dB for 25 channels after the 20-km transmission. The power penalty variation is less than 1.5 dB in the wavelength-tuning range of 20 nm. The performance of the T-ECL satisfies the requirements of the WDM-PON system.

We report a novel structure that is capable of wide wavelength tuning in the distributed Bragg reflector laser diode (DBR-LD) with a single grating mirror. This device's DBR section has two tuning elements, plasma, and heater tunings, which are implemented simultaneously on the top of a single waveguide by using an in-between dielectric layer. For the proposed structure, a three-dimensional thermal simulation was conducted. The results showed that the temperature profile within the waveguide is highly affected by the position of heater metal and thermal conductivity of the p-cladding layer. As a result, it is important to use a uniform temperature region in the DBR section for a wide tuning range and stable single-mode operation. For a 550-μm long DBR-LD with a 250-μm long DBR section, a tuning range of 26 nm (i.e., 7 nm for plasma tuning and 19 nm for heater tuning); an SMSR of more than 45 dB; and a peak power variation of less than ± 2.5 dB were obtained. From the comparisons of two DBR-LDs with only one tuning element, we confirmed that using the dielectric layer is a very effective way of achieving a wide tuning under the independent tuning operation.

Transmit–receive devices (TRD) monolithically integrated with a butt-coupled semiconductor optical amplifier (SOA) have been designed and fabricated using a buried ridge/ridge waveguide structure with low-threshold-current and high-temperature operation characteristics. The maximum output power was 31 mW under CW operation at 25 °C. At 85 °C the output power was over 9 mW with a side mode suppression of over 45 dB. The responsivity of the detector photodiode was over 0.6 A/W in the temperature range between 25 and 65 °C and over 0.3 A/W at 85 °C. It was nearly constant in the input-power range between -30 to -10 dBm.

We report the transmission capability of a tunable external cavity laser (T-ECL) that utilizes a super-luminescent diode (SLD) and a polymer Bragg reflector (PBR) operating with a direct modulation of 2.5 Gb/s for a light source of a long-reach wavelength division multiplexed-passive optical network (WDM-PON). The T-ECL successfully operated at an ambient temperature of −20 °C to 70 °C when employing a cooled SLD. A tuning range of 12-nm is achieved with a tuning power of lower than 80 mW. A side mode suppression ratio of more than 35 dB was obtained for the whole tuning range. The linewidth of the lasing spectrum is less than 0.1 nm at 20 dB from the peak power. The transmission performance of the T-ECL, including an optical bandpass filter (OBPF), is better than that of the T-ECL excluding an OBPF for a long-reach transmission over 80 km of single mode fiber (SMF). The power penalty of the T-ECL is less than 1.4 dB when using an OBPF for an 80-km transmission.

Very compact 4-channel 200-GHz-spacing external cavity lasers (ECLs) were fabricated by hybrid integration of reflection gratings and superluminescent laser diodes on a planar lightwave circuit chip. The fifth-order gratings as reflection gratings were formed using a conventional contact-mask photo-lithography process to achieve low-cost fabrication. The lasing wavelength of the fabricated ECLs matched the ITU grid with an accuracy of ±0.1 nm, and optical powers were more than 0.4 mW at the injection current of 80 mA for all channels. The ECLs showed single mode operations with more than 30 dB side lobe suppression. Keywords: High order grating, hybrid integration, external cavity laser (ECL), planar lightwave circuit (PLC), superluminescent laser diodes (SLD).

A compact-size and low-cost tunable external cavity laser transmitter optical sub-assembly with butt-coupled superluminescent diode and polymer Bragg reflector (PBR) is described. The output wavelength of the laser is widely tuned over 16 nm by a heater of the PBR and is finely tuned by a phase of the PBR. The threshold current and output power slope of the laser are 8 mA and 0.117 W/A, respectively, at the temperature of 25 °C. The directly-modulated tunable laser provides 2.5-Gb/s transmission through a 80-km standard single-mode fiber without an error-flow by controlling the phase power of the PBR and its dispersion power penalty is .

We have demonstrated a high-power widely tunable sampled grating distributed Bragg reflector (SGDBR) laser integrated monolithically with a semiconductor optical amplifier (SOA) having a lateral tapered waveguide, which is the first to emit a fiber-coupled output power of more than 10 dBm using a planar buried heterostructure (PBH). The output facet reflectivity of the integrated SOA using a lateral tapered waveguide and two-layer AR coating of TiO 2 and SiO 2 was lower than 3 × 10 - 4 over a wide bandwidth of 85 nm. The spectra of 40 channels spaced by 50 GHz within the tuning range of 33 nm were obtained by a precise control of SG and phase control currents. A side-mode suppression ratio of more than 35 dB was obtained in the whole tuning range. Fiber-coupled output power of more than 11 dBm and an output power variation of less than 1 dB were obtained for the whole tuning range.

The effects of pattern dimension on the quality of cubic SiC thin films were investigated, grown on patterned Si substrates using the chemical vapor deposition technique. Results of various characterization techniques indicated that the quality of SiC films on the patterned substrates does not noticeably improve. It was observed from high-resolution x-ray diffraction (XRD) that SiC films on scratched surfaces (≤10-nm deep) show comparable quality to SiC on flat Si, and the quality of the SiC grown on substrates with saw-tooth patterns (∼25-nm or ∼75-nm deep) might even be lower than that of the SiC/flat-Si films.

We demonstrate a 10-Gb/s tunable external cavity laser with a polymer Bragg reflector and a highly integrated semiconductor gain chip including an asymmetric ring resonator reflector. The output power of the tunable laser is increased by adjusting the coupling strengths of two multimode interferences (MMIs) of the ring resonator reflector. The output power of the tunable laser is 6 mW at gain and semiconductor optical amplifier currents of 100 mA, and at a temperature of 25°C when the cross-coupling strengths ratios of two MMI couplers are 0.36 and 0.5. The tunable laser successfully provides 10-Gb/s transmissions through 20-km standard single mode fiber (SMF). The power penalty of the tunable laser is less than 2 dB after a 20-km SMF transmission for a 16-nm tuning range. The power penalty variation is less than 2 dB during the blue-shifted wavelength tuning.

We present a ten-channel distributed feedback laser diode array (DFB-LDA) developed for the transmission of 100-Gb/s (10 x 10 Gb/s) signals separated by an 8 nm wavelength grid at a center wavelength of 1.55 mu m. For the fabrication of this type of laser array, a selective area growth (SAG) technique, electron-beam lithography, and a reverse-mesa ridge waveguide LD processing technique were adopted to offer a tailored gain spectrum to each channel, providing both accurate lasing-wavelength control and excellent single-mode yield over all channels, and reducing the fabrication cost and electrical and thermal resistances. To evaluate the operational performance of the fabricated chip systematically, we also developed a sub-assembly module containing a ten-channel lambda/4-shifted DFB-LDA, ten matching resistors, flexible printed circuit board (FPCB) wiring, and a thermistor on a metal optical bench. The static and dynamic properties of all channels of the fabricated array are examined in this paper. The developed sub-assembly module shows a side-mode suppression ratio (SMSR) of >50 dB, a modulation bandwidth of >10 GHz, and a clear eye-opening before and after a 2-km transmission with dynamic extinction ratio of >5 dB. (C) 2014 Optical Society of America

A novel InGaAsP/InP buried-ridge waveguide laser diode structure is proposed and demonstrated for use as a single-mode laser. The lateral mode of the proposed device can be controlled by adjusting the composition and thickness of the InGaAsP layer grown over the active region. Stable single-mode operation without kinks or beam-steering is achieved successfully with lateral and transverse in the junction plane even for the device with the ridge width of 9 μm up to an injection current of 500 mA. difficult to uniformly realize a ridge width of less than 3 μm by using the conventional photolithography process. To overcome this problem of conventional RWG (C-RWG) lasers, we propose a new buried-ridge waveguide (B-RWG) laser, in which lateral single-mode operation can be guaranteed even for ridge widths over 5 μm by inserting an InGaAsP layer into the ridge region. The waveguide structure of the proposed device is different from that of previously reported B-RWG lasers (8)- (10). It has been reported that B-RWG lasers have been used as high-power 0.98 μm or 1.02 μm wavelength lasers. However, there have been no reports of a high-power 1.56 μm optical- communication laser fabricated using B-RWG to our knowledge. Therefore, we have fabricated a B-RWG laser with a 9 μm ridge width, which is over 2 times larger than that of the C-RWG laser, which has ridge widths of 3 and 4 μm with the maximum condition of lateral single-mode operation. In this letter, we propose the novel B-RWG laser structure for single- mode lasers. The width and thickness of the InGaAsP layer can be controlled by photolithography and an epitaxial growing process, respectively.

We report the design and fabrication of a novel 1.55-m spot-size converter superluminescent diode (SLD) for optical access networks. The active section of SLD was fabricated by using a planar buried heterostructure to adopt the double-waveguide-core structure for low-threshold and high-output power operation at a low injection current. A ridge-based passive waveguide was employed for an efficient coupling to a planar lightwave circuit. The threshold current was as low as 14 mA, and the maximum output power was as high as 28 mW with ripple less than 3 dB at an injection current of 200 mA.

We propose and demonstrate very compact multiwavelength lasers (MWLs) with a novel configuration designed to remove the mode hopping in the modulation region and separate the wavelength-tuning of each channel for cost-effective optical line termination sources in the wavelength-division-multiplexing passive optical network. The mode hopping of MWLs in the modulation region was eliminated by wavelength trimming using a tuning heater. The MWLs operated successfully in direct modulation for 1.25-Gb/s transmission over 20 km.

We have demonstrated a very compact eight-channel 200-GHz-spacing multiwavelength laser (MWL) module for the optical line terminal source of wavelength-division-multiplexing passive optical network. The wavelength shift of MWLs and external cavity lasers from the ITU grid was within +0.14 nm for eight channels, which was well matched to the target wavelength shift of less than plusmn0.2 nm. The oscillation characteristics of our MWL module are better than those of conventional MWLs with hybrid integration.

A sampled-grating distributed Bragg reflector laser module having an integrated multiwavelength locker has been developed and evaluated. The uniquely designed wavelength locker made of thermally controlled etalon has provided uniform wavelength monitoring and very stable wavelength locking in the 188-ITU grid channels (37 nm) with 25-GHz spacing. Over the case temperature from -5/spl deg/C to 65/spl deg/C, the laser wavelength was locked within /spl plusmn/0.5 GHz, and the total power consumption of the module was less than 4 W.

We have demonstrated a high-power widely tunable sampled grating (SG) DBR laser integrated monolithically with optical semiconductor amplifier (SOA), using planar buried heterostructure (PBH). The measured threshold current was 5 mA on average with 60 chips randomly selected which is lowest among the typical average values. Fiber-coupled output power was 12.4 dBm and the output power variation was ?1 dB for the whole tuning range.

A new widely tunable laser diode structure that requires only two tuning currents is proposed. The laser diode consists of a sampled grating distributed feedback (SGDFB) laser diode monolithically integrated with a sampled grating distributed Bragg reflector (SGDBR). The phase control sections are properly inserted between the grating bursts of the SGDBR and SGDFB sections for the discrete and continuous tuning. To confirm the feasibility of the new structure, the split-step time domain model is used. The simulation result for a particular design shows that the tuning range as wide as 27 nm is possible with side-mode suppression ratio exceeding 35 dB. Furthermore, the output power is larger than that from SGDBR laser diodes with similar parameters.

We optimized the etching process for butt coupling to improve the reproducibility and the uniformity of the process for the integrated GaInAsP multiquantum-well laser with a butt-coupled waveguide. Three different ways of etching process were tested, which are reactive ion etching (RIE), RIE followed by a small amount (50 nm thick) of selective wet etching, and RIE followed by an adequate amount (125 nm thick) of selective wet etching. RIE followed by an adequate amount of selective wet etching showed the superior properties to the common expectation on RIE only, giving the measured coupling efficiency 96/spl plusmn/1.7% versus 34/spl plusmn/8%. The high coupling efficiency and the very small variation across a quarter of a 2-in wafer demonstrate that RIE coupled with an adequate amount of selective wet etching can also replace the conventional process for butt coupling, RIE followed by HBr-based nonselective wet etching, to fabricate high-quality integrated photonic devices.

We demonstrate a directly-modulated 10-Gb/s tunable external cavity laser (ECL) fabricated by using a polymer Bragg reflector and a high-speed superluminescent diode (SLD). The tuning range and output power of this ECL are measured to be >11nm and 2.6 mW (@ 100 mA), respectively. We directly modulate this laser at 10 Gb/s and transmit the modulated signal over 20 km of standard single-mode fiber. The power penalty is measured to be

We have developed a tunable external cavity laser based on the optimized superluminescent diode and a polymer Bragg reflector for C-band WDM-PON light source. The tunable laser had a wavelength tuning range of 12nm by thermo-optic tuning of the polymer waveguide at a low input power of 72 mW. This module operates successfully in direct modulation for 2.5 Gbit/s over 45 Km transmission.

We propose and demonstrate a tunable external cavity laser (ECL) composed of a polymer Bragg reflector (PBR) and integrated gain chip with gain, a ring resonator, an electro-absorption modulator (EAM), and a semiconductor optical amplifier (SOA). The cavity of the laser is composed of the PBR, gain, and ring resonator. The ring resonator reflects the predetermined wavelengths into the gain region and transmits the output signal into integrated devices such as the EAM and SOA. The output wavelength of the tunable laser is discretely tuned in steps of about 0.8 nm through the thermal-optic effect of the PBR and predetermined mode spacing of the ring resonator.

We report a high performance integrated transmit-receive-device (TRD) with a butt-coupled SOA by a well established procedure for the first time. The responsivity was same in input power range from -30 to -10dBm due to integrated SOA. The responsivity of more than 0.3 W/A was obtained until the 85degC temperature range.

This paper introduces optical devices for G-bit WDM- PON system. We have developed WDM-PON ONU employing the reflective semiconductor optical amplifier(R-SOA) and 16 ch WDM-PON OLT which is fabricated by the hybrid integration technology.

We report a 1.5 μm and 10 Gb s−1 etched mesa buried heterostructure λ/4-shifted distributed feedback laser diode (DFB-LD) for the low-cost application of WDM–based datacenter networks. To reduce the threshold current and improve the modulation bandwidth in a conventional p-/n-/p-InP current blocking structure, a thin undoped-InP (u-InP) layer was inserted between the side walls of the active region and the p-InP layer (i.e., a u-/p-/n-/p-InP structure), and the region containing the active region and the current blocking structures was etched in a mesa form (i.e., an etched mesa). From this work, it was found that a 300 μm long anti-reflection (AR)-AR DFB-LD with a mesa width of 8 μm is reduced by about 25% while a side mode suppression ratio is >50 dB and a 3 dB bandwidth is >10 GHz at a current of 40 mA; in addition, it shows a clear eye-opening with a dynamic extinction ratio of >4.5 dB at 10 Gb s−1, and a power penalty of

The butt-coupled (BT) sampled grating distributed Bragg reflector laser diode (SGDBR-LD) was designed and fabricated using planar buried heterostructure (PBH), enabling a low threshold current and a stable fundamental transverse mode. The but-coupled SGDBR-LD's with target tuning ranges of 44.4nm was fabricated, and the tuning ranges were experimentally measured to be 44.4nm. The measured peak periods of the fabricated SGDBR-LD's were well matched with theoretical values and output power is close to calculated values. The side mode suppression ratio of more than 35dB was obtained in the whole tuning range. The output power variation was less than 5dB, which is 4dB smaller than that of RWG structure.

A very compact 16-channel 200 GHz-spacing transmitter module was fabricated for wavelength division multiplexing-passive optical network (WDM-PON) optical line termination (OLT) source. The transmitters are composed of reflection gratings and hybrid integrated superluminescent laser diodes (SLD) to construct 16-channel external cavity lasers (ECLs) on the planar lightwave circuit (PLC) chip.

We have demonstrated a high-power widely tunable SG-DBR laser monolithically integrated with a SOA. The structure of SOA is a lateral tapered waveguide and a wideband AR coating. Fiber coupled output power is more than 10 dBm of CW operation, and the output power variation was /spl sim/1 dB.

We successfully fabricated a very compact 16-channel 200 GHz-spacing transmitter module for WDM-PON OLT source. The transmitters are composed of reflection gratings and hybridly integrated reflective SOAs (RSOAs) to construct 16-channel external cavity lasers(ECLs) on the PLC chip. This module operates successfully with a total throughput of 1.25 Gbit/s over 20 km transmission. (2 pages)

We report a 1.58 μm superluminescent diode (SLD) with a spot-size converter (SSC) designed and fabricated as a light source for a tunable external cavity laser (T-ECL). The active section of the SLD is fabricated by using a planar buried heterostructure (PBH) for low-threshold current and high-output power operation at a low injection current. The SSC structure of the SLD is designed to possess a buried deep-ridge waveguide (BD-RWG) and show a beam of less divergence. The full-width at half maximum (FWHM) of the horizontal and vertical far-field patterns (FFPs), due to the beam of the less divergence, are 14° and 13°, respectively. We also confirm that an L-band T-ECL employing the SSC SLD operates well enough to prove the characteristics of high performance.

We presented a hybridly-integrated tunable external cavity laser with 0.8 nm mode spacing 16 channels operating in the direct modulation of 2.5-Gbps for a low-cost source of a WDM-PON system. The tunable laser was fabricated by using a superluminescent diode (SLD) and a polymer Bragg reflector. The maximum output power and the power slope efficiency of the tunable laser were 10.3 mW and 0.132 mW/mA, respectively, at the SLD current of 100 mA and the temperature of 25 degrees C. The directly-modulated tunable laser successfully provided 2.5-Gbps transmissions through 20-km standard single mode fiber. The power penalty of the tunable laser was less than 0.8 dB for 16 channels after a 20-km transmission. The power penalty variation was less than 1.4 dB during the blue-shifted wavelength tuning.

We have fabricated a tunable external cavity laser (T-ECL) based on a superluminescent diode and a polymeric waveguide Bragg reflector, providing a cost-effective solution for wavelength division multiplexing-passive optical network (WDM-PON) systems. The wavelength of the T-ECL is tuned through 100 GHz-spacing 16 channels by the thermo-optic tuning of the refractive index of the polymer waveguide at a low input power of 70 mW. The maximum output power and the slope efficiency of the uncooled diode at 20 (75) degrees C are 8.83 (3.80) mW and 0.107 (0.061) W/A, respectively. The T-ECL operated successfully in the direct modulation for 1.25 Gbit/s transmissions over 20 km.

We have fabricated modules of 8-channel multi-wavelength lasers (MWLs) with a wavelength separation of 200 GHz for the wavelength division multiplexed-passive optical network (WDM-PON) optical line terminal sources. The variation in the output power is minimized by inserting silicone between the superluminescent diode (SLD) and the silica waveguide. The wavelength shift of each channel is less than 0.21 nm from the ITU grid and can be controlled in the range of 0.36 nm without any reductions of the output power by a tuning heater. MWLs operated successfully in the direct modulation for 1.25 Gbit/s transmissions over 20 km.

Coherent laser light was tuned by cumulative refraction of light waves in a semiconductor laser cavity, while the wavelength of electroluminescence was not tuned by any noticeable amount. This effect is explained by the fact that the laser light has perfect spatial coherence, while the electroluminescence has a spatial coherence of 0.7 µm, smaller than the width of the wavefront. The refraction angle of 2.4 deg means that more than 16 triangular electrodes are involved in the refraction. This observation of coherent tuning may lead to a new optoelectronic device, a coherent filter, which filters out only coherent light from a coherent-incoherent mixture.

Two-dimensionally arrayed nanocolumns of InGaAsP/InP were fabricated using double-exposure laser holography and reactive ion etching (RIE). The size and period of nanocolumns could be controlled accurately from 80 to 150 nm in diameter and 220 to 450 nm in period by changing the incident angle of the laser beam. RIE for a typical time of 30 min using CH 4 /H 2 plasma enhanced the aspect ratio by more than 1.5 with a slight increase of the bottom width of columns. Furthermore, a wet-treatment after RIE showed a large enhancement of photoluminescence intensity, suggesting that the damage was cured effectively on the sidewalls of the nanocolumns.