Electrooptic light modulation and second-harmonic generation in novel diazo-dye-substituted poled polymers

The nonlinear-optical susceptibilities, x/sup (2)/, of a diazo-dye-substituted polymer poled with high electric fields were determined experimentally and theoretically. The electrooptic modulation of He-Ne laser light in a traveling-wave channel-waveguide modulator using the diazo-dye-substituted poled polymer is reported, and the linear electrooptic coefficient of the poled polymer is estimated from a measured half-wave voltage. The polymer studied is a poly(methyl methacrylate) copolymerized with a methacrylate ester of the dicyanovinyl-terminated diazo dye derivative. This polymer is called 3RDCVXY. The corona-poled 3RDCVXY polymer exhibits a x/sup (2)/ value of 1*10/sup -6/ esu at 1.06 mu m. The thermal stability is excellent even at 80 degrees C. The poled 3RDCVXY polymer film shows a linear electrooptic coefficient as high as 40 pm/V at 0.633 mu m. An electrooptical light modulation in the channel 3RDCVXY polymer waveguides with a half-wave voltage as low as 5 V was obtained.<>     

Design and fabrication of zinc oxide thin-film ridge waveguides on silicon substrate with ultraviolet amplified spontaneous emission

Zinc oxide (ZnO) thin-film ridge waveguides have been designed and fabricated on n-type (100) silicon substrate. A filtered cathodic vacuum arc technique is used to deposit high-crystal-quality ZnO thin films on lattice-mismatched silicon substrates at 230/spl deg/C. A ridge waveguide of width /spl sim/2 /spl mu/m and height /spl sim/0.1 /spl mu/m is defined on the ZnO thin film by plasma etching. Room-temperature amplified spontaneous emission is observed with peak wavelength at /spl sim/385 nm under 355-nm optical excitation. It is found that the net optical gain of the ZnO thin-film ridge waveguides can be as large as 120 cm/sup -1/ at a pump intensity of /spl sim/1.9 MW/cm/sup 2/.     

Sea of polymer pillars: compliant wafer-level electrical-optical chip I/O interconnections

An electrical-optical chip input-output (I/O) interconnection technology called sea of polymer pillars (SoPP) is presented. SoPP provides highly process-integrated and mechanically flexible (compliant) electrical-optical die-to-board interconnections that mitigate thermo-mechanical expansion mismatches. The I/O density of SoPP exceeds 10/sup 5//cm/sup 2/. The compliance of the polymer pillars is shown to be 3-5 /spl mu/m/mN. Approximately 50% input optical coupling efficiency into a volume grating coupler through a set of polymer pillars is demonstrated.     

Optimized second-harmonic generation in quantum cascade lasers

Optimized second-harmonic generation (SHG) in quantum cascade (QC) lasers with specially designed active regions is reported. Nonlinear optical cascades of resonantly coupled intersubband transitions with giant second-order nonlinearities were integrated with each QC-laser active region. QC lasers with three-coupled quantum-well (QW) active regions showed up to 2 /spl mu/W of SHG light at 3.75 /spl mu/m wavelength at a fundamental peak power and wavelength of 1 W and 7.5 /spl mu/m, respectively. These lasers resulted in an external linear-to-nonlinear conversion efficiency of up to 1 /spl mu/W/W/sup 2/. An improved 2-QW active region design at fundamental and SHG wavelengths of 9.1 and 4.55 /spl mu/m, respectively, resulted in a 100-fold improved external linear-to-nonlinear power conversion efficiency, i.e. up to 100 /spl mu/W/W/sup 2/. Full theoretical treatment of nonlinear light generation in QC lasers is given, and excellent agreement with the experimental results is obtained. For the best structure, a second-order nonlinear susceptibility of 4.7/spl times/10/sup -5/ esu (2/spl times/10/sup 4/pm/V) is calculated, about two orders of magnitude above conventional nonlinear optical materials and bulk III-V semiconductors.     

Growth of metanitroaniline film crystal with controlled orientation for optical waveguide second-harmonic generation

The use of organic molecular crystals with large second-order nonlinear optical susceptibilities for implementing compact waveguide second-harmonic generation devices is addressed. The growth of metanitroaniline film crystal in a planar capillary with a channel/taper structure for single seed formation by zone melting recrystallization using a ridge heater is presented. Single-crystal film (5*15 mm/sup 2/, approximately 2- mu m thickness) was obtained with reproducible crystallographic orientation control. Cerenkov-radiation-type waveguide second-harmonic generation is demonstrated.<>     

Characterization of AZ-2415 as a Negative Electron Resist

The use of AZ-2415 as a negative electron resist is described. The effects of electron dose, optical dose, and development time on the resist line profiles are investigated. A low optical dose leads to wider and thicker developed negative lines, but with a lower contrast than lines exposed with a higher optical dose. An increase in development time results in a higher contrast which is accompanied by a significant increase in the electron dose required to maintain a fixed linewidth. A good overall process scheme would avoid both the low optical dose area and the shortest development times in favor of values of these parameters that offer greater linewidth control. Using a 0.5-/spl mu/m initial film thickness, an electron dose of 80 to 120 /spl mu/C/cm/sup 2/, an optical dose of 333 mJ/cm/sup 2/, and a 15-s development in 1:3.5 AZ-2401: H/sub 2/O produce submicrometer resist patterns that provide excellent resistance to plasma etching.     

Simultaneous enhancement of the second- and third-harmonic generations in one-dimensional semiconductor photonic crystals

We report on observation of simultaneous strong enhancements of second-harmonic generation (SHG) and third-harmonic generation (THG) in visible spectra region in a one-dimensional ZnSe-ZnMgS semiconductor photonic crystal. These enhancements come from phase matching and a high density of modes near the photonic band edge. Our result shows that the THG is due to direct /spl chi//sup (3)/ process instead of the cascaded two-step /spl chi//sup (2)/ process. Measured forward SH conversion efficiency close to 1% for only a few microns thick film demonstrates potential device applications. Theoretical calculations are in good agreement with the experimental measurements.     

Fabrication and characteristics of GaP-AlGaP tapered waveguide semiconductor Raman amplifiers

We have fabricated GaP-AlGaP tapered waveguide semiconductor Raman amplifiers, and analyzed the effect of tapering in pulse-pumped high-gain operation. The finesse measurement and 80-ps pulse pumped Raman amplification experiment were performed. Although the tapering has caused additional optical loss, the highest gain of 23 dB has been obtained for a tapered waveguide with input facet of 6.0 /spl mu/m/sup 2/ and back facet of 2.9 /spl mu/m/sup 2/ at averaged input power of 170 mW (peak power 26 W). It is shown that the optical loss of the pump light is more severe than the linear optical loss of the signal light when the gain is higher than 20 dB.     

Novel stationary-sample atomic force microscope with beam-tracking lens

An atomic force microscope with a stationary sample and a scanning cantilever using an optical lever method is demonstrated for the first time. The cantilever tip is translated to measure surface profiles while a simple lens attached to the cantilever holder guides a focused beam from a fixed collimated diode laser. The imaging capability is demonstrated up to 100*100 mu m/sup 2/.<>     

Large nonlinear optical effect in an InGaAs/InAlAs multiquantum well waveguide

All-optical refractive nonlinearity in a passive InGaAs/InAlAs multiquantum well waveguide is evaluated for TE and TM modes at 1.55 mu m wavelength and room temperature. A quarter wavelength change in the optical path length is observed at an input pump light power of 6.5 mW for 1.47 mu m wavelength in a 960 mu m long device. Nonlinear refractive index n/sub 2/ is evaluated to be -1.2*10/sup 6/ and -0.5*10-6cm/sup 2//W for the TE and the TM modes, respectively.<>     

Measurement of quadratic electro-optic effect in polydiacetylene optical waveguide

Planar optical waveguides of the soluble polydiacetylene 9-SMBU were formed by dip-coating on silicon substrates. The quadratic electro-optic (Kerr) response was measured by guided wave polarisation interferometry. The effective electro-optic coefficient was found to be 3.7*10/sup -20/ m/sup 2/V/sup -2/ at a wavelength of 1.3 mu m.<>     

Strain-compensated InGaAsSb multiple quantum-wells with digital AlGaAsSb barriers for midinfrared lasers

Midinfrared InGaAsSb-AlGaAsSb strain-compensated multiple quantum-wells (SCMQW) have been grown by solid-source molecular beam epitaxy. Short-period (AlGaAsSb)/sub y/--(AlGaSb)/sub 1-y/ digital barriers were employed to avoid growth interruptions at the barrier-well interfaces, thereby significantly improving the structural and optical properties of the InGaAsSb SCMQW as evidenced by X-ray diffraction and photoluminescence measurements. Based on these high-quality SCMQW, a room-temperature threshold current density as low as 163 A/cm/sup 2/ was achieved for 1000-/spl mu/m-long broad-area lasers emitting at 2.38 /spl mu/m in pulsed mode. The 880-/spl mu/m-long lasers retained a high characteristic temperature (T/sub 0/) of 165 K up to 80/spl deg/C and could operate at temperatures above 100/spl deg/C. A typical wavelength blueshift of 38 meV was observed in the SCMQW laser samples compared to the SCMQW-only samples.     

Infrared optical parametric oscillator in potassium titanyl phosphate

An infrared optical parametric oscillator using potassium titanyl phosphate (KTP) pumped by a 1.06- mu m Nd:YAG laser is discussed. Oscillation was obtained around the degenerate wavelength at 2.12 mu m with a pump threshold of 40 MW/cm/sup 2/ in a 30-ns pulse. Difference frequency generation with an output at 2.4 mu m was also obtained between inputs at 1.06 and 1.9 mu m. The broad tuning range and high damage resistance of KTP make this an important new source of tunable infrared radiation.<>     

1.49-/spl mu/m-band gain-shifted thulium-doped fiber amplifier for WDM transmission systems

This paper describes in detail the amplification characteristics of gain-shifted thulium-doped fiber amplifiers (GS-TDFAs) operating in the 1480to 1510-nm wavelength region (1.49-/spl mu/m S-band) for use in wavelength-division-multiplexing (WDM) systems. Gain shifting of a TDFA, which normally has a gain band at 1.47 /spl mu/m (S/sup +/-band), is achieved by two types of dual-wavelength pumping: (1) 1.05 and 1.56 /spl mu/m or (2) 1.4 and 1.56 /spl mu/m. The main pump source at 1.05 or 1.4 /spl mu/m creates population inversion between /sup 3/F/sub 4/ (upper laser level) and /sup 3/H/sub 4/ (lower laser level), while the auxiliary pump source at 1.56 /spl mu/m reduces the average fractional inversion down to approximately 0.4, which is a desired level for gain shifting. We show experimentally that the former provides a low internal noise figure (<4 dB) due to high fractional inversion at the input end of a thulium fiber, while the latter provides a very high optical efficiency but a higher internal noise figure (/spl sim/5 dB) due to the lower fractional inversion at the input end. These characteristics were verified by numerical simulation based on a comprehensive rate equation modeling. We demonstrated a 1.4- and 1.56-/spl mu/m laser-diode-pumped GS-TDFA with an optical efficiency of 29.3% and high output power of +21.5 dBm. Gain flatness and tilt control were also investigated. These results strongly confirm the feasibility of using GS-TDFAs in practical ultralarge-capacity WDM networks.     

High-power nearly diffraction-limited AlGaAs-InGaAs semiconductor slab-coupled optical waveguide laser

Beam-quality measurements on the output of a 915-nm AlGaAs-InGaAs-GaAs slab-coupled optical waveguide laser (SCOWL) are reported. This device had a nearly circular mode (3.8 /spl mu/m by 3.4 /spl mu/m 1/e/sup 2/ widths in the near-field) and was capable of a single-ended continuous-wave output power of greater than 1 W. Measurements of M/sup 2/ indicate that the SCOWL output beam is nearly diffraction-limited in both directions with M/sub x//sup 2/ /spl sim/ M/sub y//sup 2/ /spl sim/ 1.1 over the entire range of output powers measured.     

Comparative determinations of the /spl chi//sup (2)/ spatial distribution induced in thermally poled silica planar samples

We herein report the comparison of two independent reconstructions of the distribution of the /spl chi//sup (2)/ nonlinear susceptibility induced by thermal poling in planar silica samples. Both nonlinear profiles are quantitatively in good agreement in terms of /spl chi//sup (2)/ magnitude and nonlinear thickness; and qualitatively in agreement in terms of shape. We conclude that both characterization methods used are efficient for the determination of the /spl chi//sup (2)/ susceptibility spatial distribution in bulk samples.     

Continuous-wave operation of GaInAs-AlGaAsSb quantum cascade lasers

We report on the demonstration of continuous-wave (CW) operation of GaInAs-AlGaAsSb quantum cascade (QC) lasers. By placing a 2.5-/spl mu/m-thick gold layer on both sides of the laser ridge to extract heat from the active region in the lateral direction, together with mounting the device epilayer down, we have achieved CW operation of GaInAs-AlGaAsSb QC lasers composed of 25 stages of active/injection regions. The maximum CW operating temperature of the lasers is 94 K, and the emission wavelength is around /spl lambda//spl sim/4.65 /spl mu/m. For a device with the size of 10/spl times/2000 /spl mu/m/sup 2/, the CW optical output power per facet is 13 mW at 42 K and 4 mW at 94 K. The CW threshold current density is 1.99 kA/cm/sup 2/ at 42 K, and 2.08 kA/cm/sup 2/ at 94 K, respectively.     

Photoelectric instability in optical fibre resulting in spontaneous second harmonic generation

The self-organised second harmonic generation (SHG) in optical fibres is explained as a consequence of a convective instability leading to spontaneous formation of the chi /sup (2)/ grating due to the growth of small fluctuations. The authors show that the observed SHG should be interpreted as amplification of noise.<>     

Experimental determination of carrier-induced differential loss in 2-section GaInAsP/InP laser-waveguide

Measurements of threshold current density and external efficiency on broad-area laser-waveguide structure have led to the determination of the optical loss and differential loss d alpha /dN approximately=1.1-2.3 *10/sup -17/ cm/sup 2/ at lambda =1.53 mu m in a lambda /sub g/=1.30 mu m GaInAsP layer. This measurement will be useful for the design of tunable lasers.<>     

1.65 /spl mu/m-band optical amplification with Er/sup 3+/-doped fluorozirconate fibre using 0.8 /spl mu/m upconversion pumping

In order to expand the available bandwidth for wavelength division multiplexing transmission systems, a 1.65 /spl mu/m-band optical fibre amplifier with Er/sup 3+/-doped fluorozirconate fibre using 0.8 /spl mu/m upconversion pumping has been demonstrated. The positive gain, 3.8 dB, is the first ever achieved by means of (/sup 2/H/sub 11/2/, /sup 4/S/sub 3/2/) /spl rarr/ /sup 4/I/sub 9/2/ stimulated emission transition.