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A total of 1,257 gilts were used to de- termine the effect of space allowance during rearing and age at puberty on total pigs produced and removal rate over 3 parities. There were 2 treatments. In treat- ment 1, gilts were given a space allowance of 1.13 m 2 / gilt (15 gilts per pen), and in treatment 2, gilts were given 0.77 m 2 /gilt (22 gilts per pen). Gilts (38 kg and 75 d of age) were individually weighed upon entry and before leaving the rearing site. They were scanned for backfat thickness and loin depth and had their feet and legs scored for structure, movement, and toe evenness before leaving the rearing site. Commencing at approx- imately 140 d of age, gilts were exposed to a vasecto- mized boar once daily with age of puberty recorded for all gilts attaining puberty before leaving the rearing site. Gilts were then moved to a specialized gilt breed- ing farm. When confirmed pregnant, they were moved to 1 of 9 sow farms at random, where gilts remained until removal from that herd. Space allowance in rear- ing had no effect (P > 0.29) on growth rate in rearing, backfat thickness and loin depth, total pigs produced, or removal rate. A greater percentage of gilts attained puberty (P = 0.02) and attained puberty at a younger age (P 860 g/d) had greater (P 260 d of age, whereas a greater (P 280 d of age were removed by the end of parity 3. In conclusion, space allowance in rearing did not affect total pigs produced or removal rate; however, gilts that attained puberty at a younger age produced more pigs over parities 1 to 3.

The objective of this study was to evaluate targeted maternal weight gains in sows by parity group during gestation. Weight and backfat gains during gestation by parity, weight, and backfat groups also were analyzed. The data evaluated were a subset (374 sows) of a larger experiment that compared three methods of feeding sows during gestation on weight and backfat gains and subsequent reproductive performance. Feed allowances were based on modeled calculations of energy and nutrient requirements to achieve target sow maternal weight and backfat gains. Actual backfat gain for gilts and sows was regressed on maternal weight gain and estimated energy available for gain. The regression equations were then used to predict maternal weight gains for target backfat gains for three parity groups (gilts, Parity 1 and 2 sows, and Parity 3 and older sows). For gilts and Parity 1 and 2 sows, much greater target maternal weight gains are required to achieve 6 and 9 mm of backfat gain, whereas Parity 3 and older sows require maternal weight gains similar to those targeted to achieve the desired backfat gain. Given similar energy intake levels above maintenance, gilts gained more weight than multiparous sows, as gain was based more on protein and less on fat and thus was more efficient. Gilts required more maternal weight gain than sows to achieve similar backfat gains due to the higher protein and low fat contents of gain in younger, lighter sows compared with older parity sows. Low-backfat sows that needed to gain large amounts of backfat failed to achieve these large gains. We speculate this failure may be due to lower tissue insulation levels with the low backfat levels and higher activity levels of these sows compared with high-backfat sows. It seems that both parity and weight are individually important factors that influence energy and nutrient requirements for gestation in the modern sow.

A total of 684 sows from breeding groups over 6 wk was used to compare three methods of feeding during gestation on gestation and lactation performance. Control gilts and sows were fed according to body condition based on a scale of 1 to 5 (1 = thin, 5 = fat). Sows were visually assessed for body condition at breeding and were assigned a daily feed allowance to achieve a BCS of 3 at farrowing. Treatment 2 used feeding levels based on backfat thickness (measured between d 0 and 5 after breeding) and weight at weaning for sows or service for gilts. Feed allowance was calculated to achieve a target backfat of 19 mm at farrowing, and remained constant from d 0 to 101 of gestation. Feed allowances were based on modeled calculations of energy and nutrient requirements to achieve target sow maternal weight and backfat gains. Treatment 3 was identical to Treatment 2, except that feeding pattern was altered for thin sows and gilts ( 21 mm), but no difference in the percentage of thin sows ( 21 mm) at farrowing compared with sows with

Twelve multiparous sows with an average initial weight of 182 kg were used in a randomized complete block design to determine the effects of feeding Carnichrome (50 mg of carnitine and 200 microg of chromium picolinate per kilogram of feed, as fed) on energy and nitrogen utilization in early, mid-, and late gestation. All sows were fed a diet with or without Carnichrome for the preceding 28-d lactation, the weaning-to-estrus period, and for the duration of gestation. Daily feeding allowances over pregnancy were based on calculated energy and nutrient requirements to achieve a target sow maternal weight gain of 20 kg and remained constant throughout gestation. Heat production (HP) and its partitioning (activity, thermic effect of feeding short term [TEFst], basal) were determined in early (wk 5 or 6), mid- (wk 9 or 10), and late (wk 14 or 15) pregnancy using indirect calorimetry. Net maternal weight gain and total number of fetuses averaged 21.6 kg and 16.4, respectively. Organic matter and energy digestibility for the Carnichrome diet was greater (P < 0.05), which resulted in greater DE and ME contents (0.6%, P < 0.05) compared with the control diet. The digestibility coefficient of energy in the current experiment for a typical corn and soybean meal diet (92%) was greater than that predicted from DE values of corn and soybean meal in feeding tables (88%). Carnichrome had no effect on total HP, energy retained as protein or lipid, and maternal energy retention in early, mid-, or late gestation. Heat production in late gestation increased linearly (4.0 kJ/[kg BW0.75 x d]) for each additional day from d 90 to 110, despite the reduction of ME intake per unit of BW0.75. Metabolizable energy requirement for maintenance was 405 kJ/(kg BW0.75 x d). On average, activity HP was 116 kJ/(kg BW0.75 x d), which was equivalent to 20% of ME intake; however, this value ranged from 11 to 37% between sows, which corresponds to duration of standing ranging from 210 to 490 min/d. Energy cost of standing activity averaged 0.30 kJ/(kg BW0.75 x min). In conclusion, Carnichrome had no effect on the components of heat production and maternal weight gain during gestation, although it improved energy and organic matter digestibility of the diet.

BMS-200475, a novel carbocyclic analog of 2′-deoxyguanosine, is a potent inhibitor of hepatitis B virus in vitro (ED50 = 3 nM) with relatively low cytotoxicity (CC50 = 21–120 μM). A practical 10-step asymmetric synthesis was developed affording BMS-200475 in 18% overall chemical yield and >99% optical purity. The enantiomer of BMS-200475 as well as the adenine, thymine, and iodouracil analogs are much less active.

Dietary inclusion of co-products (Co-P) provides opportunities for diversifying the feedstuff matrix by using local feedstuffs, reducing feed costs, and producing value-added pork. In 2 studies, we determined effects of Co-P (canola meal, distillers dried grains with solubles, and co-extruded oil seed and field pea) inclusion level and reduced dietary CP concentration on growth performance, carcass characteristics, and jowl fatty acid profiles of growing-finishing pigs. Pigs were fed isoenergetic and isolysinic diets over 4 growth phases with 8 pen observations per dietary regimen. At slaughter, carcasses were characterized for all pigs and jowl fat was collected from 2 pigs per pen. In Exp. 1, 1,056 pigs (initial BW, 35.3 ± 0.4 kg) were fed 3 levels of dietary Co-P (low, mid, and high) and 2 CP concentrations (low and normal). Overall (d 0 to 86), increasing Co-P inclusion from low to mid or high decreased (P0.001) ADFI and ADG of pigs. Low CP concentration increased (P0.05) ADFI and ADG compared with normal CP concentration. An interaction (P = 0.026) occurred between dietary Co-P inclusion and CP concentration for G:F; low CP reduced (P0.05) G:F compared with normal CP for pig fed low Co-P, but G:F did not differ between CP concentrations for pigs fed mid and high Co-P. Increasing dietary Co-P inclusion from low to high increased (P0.001) α-linolenic acid (ALA) in jowl fat but decreased (P0.001) carcass weight and loin depth. In Exp. 2, 1,008 pigs (initial BW, 30.3 ± 0.4 kg) were assigned to 5 dietary regimens with Co-P increasing from 2.0 to 50.0% or a sixth regimen with 10% extra supplemental AA for the 37.5% Co-P diet. Overall (d 0 to 97), increasing Co-P inclusion did not affect ADFI, ADG, and G:F. Increasing dietary Co-P inclusion linearly decreased (P0.01) carcass weight, dressing percentage, backfat thickness, and loin depth but linearly increased (P0.001) jowl ALA. Supplementing 10% extra AA to the 37.5% Co-P diet did not affect growth performance or dressing percentage but increased (P = 0.014) carcass leanness and decreased (P = 0.023) backfat thickness compared with the 37.5% Co-P diet, indicating that dietary AA supply did not limit BW gain. In conclusion, Co-P can be included by up to 50% in diets for growing-finishing pigs without affecting G:F. However, increasing dietary Co-P may reduce ADG, ADFI, and carcass weight even if diets are balanced for dietary NE and standardized ileal digestible AA content.

Twenty-eight right-handed, young adults participated in a sensory testing experiment to evaluate spatial resolution at 10 positionally matched sites on the right- and left-hand sides of the face. An adaptive psychophysical (i.e. tracking) procedure was used to estimate the threshold spatial separation for perceiving two points of contact at each site. Estimates of the threshold at one site on both sides of the face were also obtained with a method-of-limits procedure similar to that employed for clinical evaluation of patients. In addition, each individual was asked to rate (i) his(her) overall facial sensitivity to touch and (ii) the degree to which he(she) could discern subtle changes in lip, cheek and chin position during speech, chewing and facial expression. Analysis of the estimates of the threshold separation obtained with the tracking procedure revealed a significant effect of gender (p0.04) and of site (p0.001). Females were more spatially sensitive than males: average threshold separations were 1.55 mm less. Most notably, the threshold increased ninefold with distance posterolaterally from the oral opening. The vermilion of the upper lip was the most spatially sensitive site (population geometric mean = 2.4 mm) and the preauricular skin the least spatially sensitive site (20.9 mm). Significant effects of side and of interactions among gender, side and site were not observed. The estimates obtained with the method-of-limits procedure were very similar to those obtained with the tracking procedure: the latter were 0.67 mm less on the average. Individuals' ratings of overall facial sensitivity to touch were similar for males and females (p0.70). Females, however, reported greater ability to discern subtle changes in lip, cheek and chin position than males (p0.03). The ratings of this sensory function correlated negatively with the estimates of the threshold separation on the vermilion of the upper lip (p0.03).

Expeller-pressed (EP) canola meal contains more residual oil than solvent-extracted canola meal and might be an attractive feedstuff for swine, but it has been poorly characterized. In Exp. 1, six ileal-cannulated barrows (36 kg of BW) were fed at 3x maintenance either a 44% EP canola meal diet or a N-free diet in a crossover design to measure energy and AA digestibility and calculate standardized ileal digestible (SID) AA and NE content, with 6 observations per diet. Each period consisted of a 5-d diet adaptation and a 2-d feces and 3-d digesta collection. The EP canola meal contained (% of DM) 38.5% CP, 13.3% ether extract, 2.42% Lys, 1.54% Thr, 0.62% Met, and 23.2 micromol/g of glucosinolates. Apparent total tract energy digestibility was 75.0% and the DE and predicted NE content were 3.77 and 2.55 Mcal/kg (in DM), respectively. The SID AA content (% of DM) was 1.77% Lys, 1.04% Thr, and 0.52% Met. In Exp. 2, a total of 1,100 pigs (25 kg of BW) housed in 50 pens were fed 5 dietary regimens with 0, 7.5, 15, and 22.5% or decreasing amounts (22.5, 15, 7.5, and 0%, respectively) of EP canola meal over 4 phases to validate performance and carcass characteristics. Diets were formulated to contain equal NE:SID Lys for each growth phase (g/Mcal; 4.04, d 0 to 25; 3.63, d 26 to 50; 3.23, d 51 to 77; 2.83, d 78 to 90). At slaughter, carcass characteristics were measured for all pigs, and jowl fat was sampled for 2 pigs per pen. For d 51 to 90, the 22.5% EP canola meal regimen was reduced to 18% (22.5/18%) because of decreased ADFI in phases 1 and 2. Overall (d 0 to 90), increasing dietary EP canola meal linearly decreased (P0.001) ADG and ADFI and linearly increased (P0.01) G:F. For 0 and 22.5/18% EP canola meal, respectively, ADG was 978 and 931 g/d, ADFI was 2.77 and 2.58 kg/d, and G:F was 0.366 and 0.378. Increasing dietary EP canola meal did not alter the carcass backfat thickness, loin depth, or jowl fat fatty acid profile. Pigs fed 22.5/18% EP canola meal reached slaughter weight 3 d after (P0.05) pigs fed 0% EP canola meal. In summary, EP canola meal provided adequate energy and AA; however, ADG was reduced by 3 g/d per 1% of EP canola meal inclusion, likely because of increased dietary glucosinolates. Thus, the amount of EP canola meal included in swine diets should be targeted to an expected growth performance and carcass quality. Finally, diets formulated to contain an equal NE and SID AA content did not entirely eliminate the risks for reduced growth performance associated with inclusion of an alternative feedstuff.

We study the nonlinear properties of bulk AlGaAs and GaAs/AlGaAs multiple quantum wells(MQW) below the half‐band‐gap energy using subpicosecond pulses between 1.65 and 1.7 μm. In the bulk material we find a value for the nonlinear index n 2 = +3.6× 10−14 cm2/W and a two‐photon absorption coefficient β = 0.26 × 10−4 cm/MW. In the MQW we measure an n 2 up to 2.4 times larger, and we attribute this enhancement to a stronger 1S‐exciton intermediate state. The β value is up to 25 times larger in the MQW. This larger value may result from midgap states that resonantly enhance the virtual intermediate state in two‐photon absorption and act as a real transition in a two‐step absorption process. The resulting figure of merit (2n 2/βλ) for the bulk (MQW)material is 17 (1.6), which means that these semiconductors below half band gap are appropriate for all‐optical switching and quantum optics applications. We confirm that n 2 is instantaneous on the 300 fs time scale of our pulses from self‐phase‐modulation spectra as well as time‐resolved pump‐probe measurements. However, we find an intriguing exchange of energy between the two orthogonal axes as evidenced by the signal along the probe axis following the negative derivative of the pump intensity. This result may be explained by self‐phase modulation of the pump combined with a low‐frequency Raman process that couples the modes along orthogonal axes.

A total of 1,257 gilts were used to determine the effect of space allowance during rearing and age at puberty on total pigs produced and removal rate over 3 parities. There were 2 treatments. In treatment 1, gilts were given a space allowance of 1.13 m(2)/gilt (15 gilts per pen), and in treatment 2, gilts were given 0.77 m(2)/gilt (22 gilts per pen). Gilts (38 kg and 75 d of age) were individually weighed upon entry and before leaving the rearing site. They were scanned for backfat thickness and loin depth and had their feet and legs scored for structure, movement, and toe evenness before leaving the rearing site. Commencing at approximately 140 d of age, gilts were exposed to a vasectomized boar once daily with age of puberty recorded for all gilts attaining puberty before leaving the rearing site. Gilts were then moved to a specialized gilt breeding farm. When confirmed pregnant, they were moved to 1 of 9 sow farms at random, where gilts remained until removal from that herd. Space allowance in rearing had no effect (P0.29) on growth rate in rearing, backfat thickness and loin depth, total pigs produced, or removal rate. A greater percentage of gilts attained puberty (P = 0.02) and attained puberty at a younger age (P0.01) when given the greater space allowance in rearing. Gilts given the lower space allowance in rearing had more (P = 0.04) cracks on their rear hooves. Gilts attaining puberty at a younger age (185 d) had a greater growth rate in rearing, greater backfat thickness at 200 d of age, and produced more (P0.05) pigs over parities 1 to 3. Gilts in the fastest growth-rate group in rearing (860 g/d) had greater (P0.05) total born in parity 1, but total pigs produced to the end of parity 3 was not different (P = 0.47). Contrary to expectation, a fast growth rate in rearing did not negatively affect removal rate. Gilts served between 240 to 260 d of age produced more (P0.01) pigs by the end of parity 3 than those served at260 d of age, whereas a greater (P0.01) percentage of gilts served at280 d of age were removed by the end of parity 3. In conclusion, space allowance in rearing did not affect total pigs produced or removal rate; however, gilts that attained puberty at a younger age produced more pigs over parities 1 to 3.

The balanced operation of a multiple-quantum-well balanced heterodyne receiver photonic integrated circuit (PIC) is described. Using only SMA-connected 50 Omega commercial electronics, a free-space beam sensitivity of -42.3 dBm at 108 Mb/s and -39.7 dBm at 200 Mb/s for NRZ FSK (frequency-shift keying) reception has been achieved. This represents a 14 dB improvement over any previous heterodyne receiver PIC sensitivity. In addition to providing the multichannel benefits of heterodyne reception, this is also the highest sensitivity yet reported for any OEIC (optoelectronic integrated circuit) receiver. >

Active mode-locking of a broadly tunable monolithic semiconductor laser based on a grating assisted vertical coupler filter resulted in 10 - 12 ps pulses at a repetition rate of 15.8 GHz. Mode-locking was achieved at discrete wavelengths from 1544.5 nm to 1564.7 nm.

The objective of this study was to evaluate targeted maternal weight gains in sows by parity group during gestation. Weight and backfat gains during gestation by parity, weight, and backfat groups also were analyzed. The data evaluated were a subset (374 sows) of a larger experiment that compared three methods of feeding sows during gestation on weight and backfat gains and subsequent reproductive performance. Feed allowances were based on modeled calculations of energy and nutrient requirements to achieve target sow maternal weight and backfat gains. Actual backfat gain for gilts and sows was regressed on maternal weight gain and estimated energy available for gain. The regression equations were then used to predict maternal weight gains for target backfat gains for three parity groups (gilts, Parity 1 and 2 sows, and Parity 3 and older sows). For gilts and Parity 1 and 2 sows, much greater target maternal weight gains are required to achieve 6 and 9 mm of backfat gain, whereas Parity 3 and older sows require maternal weight gains similar to those targeted to achieve the desired backfat gain. Given similar energy intake levels above maintenance, gilts gained more weight than multiparous sows, as gain was based more on protein and less on fat and thus was more efficient. Gilts required more maternal weight gain than sows to achieve similar backfat gains due to the higher protein and low fat contents of gain in younger, lighter sows compared with older parity sows. Low-backfat sows that needed to gain large amounts of backfat failed to achieve these large gains. We speculate this failure may be due to lower tissue insulation levels with the low backfat levels and higher activity levels of these sows compared with high-backfat sows. It seems that both parity and weight are individually important factors that influence energy and nutrient requirements for gestation in the modern sow.

A total of 684 sows from breeding groups over 6 wk was used to compare three methods of feeding during gestation on gestation and lactation performance. Control gilts and sows were fed according to body condition based on a scale of 1 to 5 (1 = thin, 5 = fat). Sows were visually assessed for body condition at breeding and were assigned a daily feed allowance to achieve a BCS of 3 at farrowing. Treatment 2 used feeding levels based on backfat thickness (measured between d 0 and 5 after breeding) and weight at weaning for sows or service for gilts. Feed allowance was calculated to achieve a target backfat of 19 mm at farrowing, and remained constant from d 0 to 101 of gestation. Feed allowances were based on modeled calculations of energy and nutrient requirements to achieve target sow maternal weight and backfat gains. Treatment 3 was identical to Treatment 2, except that feeding pattern was altered for thin sows and gilts (15 mm at service) in an attempt to reach 19 mm by d 36 of gestation. Sows were weighed at the previous weaning, and gilts were weighed at service, with both weighed again between d 112 and 114 of gestation. Backfat was measured between d 0 and 5, and again between d 108 and 113 of gestation. At farrowing, sows on Treatments 2 and 3 had 19 and 19.1 mm of backfat, respectively, whereas control sows tended to have greater (P0.07) backfat (20 mm). On average, sows targeted to gain 6 to 9 mm of backfat failed to reach target gains regardless of feeding method. Feeding sows in gestation based on backfat (Treatments 2 and 3) resulted in a numerically higher proportion of sows in the target backfat range of 17 to 21 mm (40.2, 53.3, and 52.6% for control and Treatments 2 and 3, respectively) at farrowing and a numerically lower percentage of fat sows (21 mm), but no difference in the percentage of thin sows (17 mm) compared with feeding based on body condition. In conjunction with this observation, sows fed based on BCS were fed higher (P0.05) feeding levels in gestation than were sows fed based on backfat depth. Gestation feeding method had no effect on performance during lactation. Feed intake in lactation was lower (P0.05) for high backfat sows (21 mm) at farrowing compared with sows with21 mm. The high proportion of sows in the optimal backfat category demonstrates that feeding based on backfat and BW has potential for facilitating more precise feeding during gestation.

Twelve multiparous sows with an average initial weight of 182 kg were used in a randomized complete block design to determine the effects of feeding Carnichrome (50 mg of carnitine and 200 microg of chromium picolinate per kilogram of feed, as fed) on energy and nitrogen utilization in early, mid-, and late gestation. All sows were fed a diet with or without Carnichrome for the preceding 28-d lactation, the weaning-to-estrus period, and for the duration of gestation. Daily feeding allowances over pregnancy were based on calculated energy and nutrient requirements to achieve a target sow maternal weight gain of 20 kg and remained constant throughout gestation. Heat production (HP) and its partitioning (activity, thermic effect of feeding short term [TEFst], basal) were determined in early (wk 5 or 6), mid- (wk 9 or 10), and late (wk 14 or 15) pregnancy using indirect calorimetry. Net maternal weight gain and total number of fetuses averaged 21.6 kg and 16.4, respectively. Organic matter and energy digestibility for the Carnichrome diet was greater (P0.05), which resulted in greater DE and ME contents (0.6%, P0.05) compared with the control diet. The digestibility coefficient of energy in the current experiment for a typical corn and soybean meal diet (92%) was greater than that predicted from DE values of corn and soybean meal in feeding tables (88%). Carnichrome had no effect on total HP, energy retained as protein or lipid, and maternal energy retention in early, mid-, or late gestation. Heat production in late gestation increased linearly (4.0 kJ/[kg BW0.75 x d]) for each additional day from d 90 to 110, despite the reduction of ME intake per unit of BW0.75. Metabolizable energy requirement for maintenance was 405 kJ/(kg BW0.75 x d). On average, activity HP was 116 kJ/(kg BW0.75 x d), which was equivalent to 20% of ME intake; however, this value ranged from 11 to 37% between sows, which corresponds to duration of standing ranging from 210 to 490 min/d. Energy cost of standing activity averaged 0.30 kJ/(kg BW0.75 x min). In conclusion, Carnichrome had no effect on the components of heat production and maternal weight gain during gestation, although it improved energy and organic matter digestibility of the diet.

Using tensile‐strained InGaAs/InGaAsP multiple quantum well material to increase the gain bandwidth, we demonstrate a tuning range of 74.4 nm with sidemode‐suppression ratio of ≳25 dB and as high as 34 dB in a broadly tunable vertical‐coupler filtered laser at 1.55 μm. Due to its wide gain bandwidth and significant gain‐peak shift to shorter wavelengths with gain current increase, the tensile‐strained quantum well material is well suited for broadly tunable lasers.

An InP based 1×16 optical switch is demonstrated. The sixteen output ports are spaced 250 μm apart, and the total device length is 5.9 mm. Optical amplifiers are used to gate the optical signals and to provide optical gain. The total loss of the device, excluding coupling, is less than 2.5 dB and loss free operation was observed at low input powers. The output extinction ratios are lower than 18 dB and the uniformity spread of the sixteen channels is as low as 6.7 dB.

Broadly tunable semiconductor lasers are important sources for a number of applications, especially wavelength division multiplexed networks and switching systems. Presently, the most developed monolithic tunable lasers, the distributed feedback (DFB) or distributed Bragg reflector (DBR), are limited to an ~10nm electrical tuning range. By integrating a grating-assisted vertical coupler as a tunable intracavity filter in a novel active/passive monolithic laser, we have achieved a measured tuning range of 57nm.

We report the first demonstration of narrowband (

A new mechanism for polarization rotation in rib waveguides is suggested and demonstrated in InP waveguides. The polarization rotation is achieved by loading a rib waveguide in a periodic asymmetric way. Complete TE↔TM conversion, with only 2–3 dB excess loss, is obtained in a 3.7‐mm‐long InP loaded waveguide. Strong polarization rotation (80%), in shorter devices (0.3 mm long), is also demonstrated.

We describe integration of lasers and optical amplifiers at 1.3 μm wavelength. The effects of the residual mirror reflectivity at the amplifier front facet are discussed. Using photonic integration techniques very high coupling efficiency of light from the laser to the amplifier sections was observed, with current transfer efficiency (ratio of photocurrent to drive current) as high as 33%. The output light current characteristics of the laser have a slope efficiency higher than 2 mW/mA. This device may be used for digital modulation with very low rf power drive requirements. Modulation at 2 Gbit/s has been demonstrated.

Using bulk InGaAsP as a saturable absorber we have passively mode locked a NaCl color center laser to produce transform‐limited, pedestal‐free pulses near 1.6 μm as short as 197 fs with up to 4.2 kW peak power. Our results simplify the saturable absorber material requirements and prove that excitons are not required for generating subpicosecond pulses. By comparing a dozen samples we find that a minimum band‐edge absorbance of 40% is required to generate subpicosecond pulses, although details of the band edge are not critical. In addition, we find stable mode locking always occurs on the long‐wavelength side of the laser gain peak.

Alternative approaches for developing 2.0- 2.5 um single frequency semicondoctor lasers are reviewed.

Lasers play a key role in a wide variety of applications relevant to NASA missions and instruments. These include such diverse areas as spectroscopy, communications, signal processing, metrology and micro-instruments. The unique characteristics of lasers including high optical power in a narrow wavelength range, small beam divergence, phase coherence, and high-frequency modulation, make lasers ideal sources for many of these applications. However, the large size, high power requirements, and relative fragility of conventional gas and solid-state lasers have limited their usefulness for many spaceborne instruments. With the advent of semiconductor lasers, it is now possible to fabricate much smaller, higher efficiency lasers and laser instruments, making them practical choices for a wide variety of applications in space missions. Semiconductor lasers also offer orders-of-magnitude increases in communication bandwidth which enables tremendous enhancements in spacecraft to ground and inter-instrument data tr...

Rapid reverse-phase analytical and preparative HPLC methods have been developed for application to parallel synthesis libraries. Gradient methods, short columns, and high flow rates allow analysis of over 300 compounds per day on a single system, or purification of up to 200 compounds per day on a single preparative system. Hardware and software modifications allow continuous unattended use for maximum efficiency and throughput.

The use of N-frequency tunable distributed Bragg reflector (DBR) lasers has been suggested for WDM switching and routing networks [1-2]. Such networks will tune lasers to different optical frequencies, to enhance the transmission capacity through optical fibers, and also to direct optical signals to different destinations. The networks presently under consideration will have 10-20 frequency channels, with 50-100 GHz (4.05-8.1 A) channel spacing in the 1.54-1.56 micron wavelength window. If DBR lasers are to be used, it is critically important to establish that the tuning mode spacing of the lasers is constant, and can be reproduced with a high degree of accuracy, so that a constant channel allocations can be maintained throughout the system. For each laser being used, a tuning curve must be established. At present, it can be measured by means of a wavemeter or an optical spectrum analyzer. The tuning curve shows the optical frequency of the laser vs. the current applied to the tuning (grating) section, and determines the different currents that should be applied to address the different frequencies.

Semiconductor ring lasers are attractive, by the nature of their geometry, for short pulse generation through active mode-locking and colliding pulse mode-locking (CPM). However, to date, only CW operation of small diameter ring lasers in GaAs has been demonstrated. Recent advances in InP fabrication technology have enabled the realization of complex photonic integrated circuits using multiple quantum well (MQW) active regions and low-loss passive waveguides. Using these techniques, we have fabricated an 3.0-mm diameter InGaAsP MQW ring laser which is actively mode-locked at 9.0 GHz producing nearly transform limited 27 ps optical pulses.

We demonstrate formation of buried InGaAsP/InP quantum well waveguides by means of phosphorous ion implantation and thermal annealing during regrowth. We use absorption spectra of implanted and unimplanted regions to estimate the induced index difference, which is on the order of 1 % at 1.55 μm. Calculated mode intensities are in good agreement with the observed near field intensity patterns. With this etchless implant technique, we achieve a significant reduction in propagation loss for single-mode p-i-n waveguides relative to etched semi-insulating planar buried heterostructure waveguides fabricated from the same quantum well structure. This type of band-gap engineering, with its simplicity and high yield, lends itself to the fabrication of complex integrated optoelectronic circuits. These include integrated laser/modulators and switch arrays.

High-speed Mach-Zehnder (MZ) intensity modulators are critical components in long-haul, high-bit-rate optical fiber communications systems at 1.55 µm. Here MZ modulators have a clear advantage over directly modulated injection lasers and external electroabsorption modulators since the wavelength chirp can be tuned in MZs to compensate for fiber dispersion. Although much recent progress has been made in monolithic integration of electroabsorption modulators with lasers, an electrorefractive MZ modulator with optical gain has not yet been reported.

Heterodyne receiver photonic integrated circuits (PIC’s), incorporating continuously tunable local oscillator (LO) lasers, directional couplers and photodetectors, offer the potential for dramatic simplification of coherent lightwave technology by eliminating the coupling and packaging of the corresponding discrete devices[1,2].

The use of tapered waveguides to adiabatically increase the lateral and transverse mode size of a semiconductor laser has been recently demonstrated, and improved tolerances for coupling into a single-mode fiber were reported.1 The adiabatic-mode-expansion (AME) waveguide of the previous work was part of the Fabry–Perot laser cavity.

Optical coupling of a semiconductor laser to a single-mode optical fiber using lensed fiber requires submicrometer alignment accuracy and leads to difficult packaging problems. Here we demonstrate the application of photonic integrated circuit (PIC) technology by using ultra-thin stop-etch epitaxial layers to integrate a controlled vertically tapered passive waveguide in a multiple quantum-well (MQW) laser cavity. This tapered waveguide adiabatically expands the mode size at the output to provide a better match to a single-mode fiber.

Because of the increasing interest in long-wavelength devices operating in the 1.1–1.55-μm wavelength region, growth techniques such as organometallic vapor-phase epitaxy (OMVPE) and chemical-beam epitaxy (CBE) are required to use toxic hydrides such as AsH3 and PH3 as the source of group V precursors. Of the two hydrides, AsH3 is more toxic, having a daily 8-h exposure limit of only 50 parts per billion, which requires the installation of elaborate safety systems prior to any growth. As a result, there have been many attempts to replace arsine with metal-organic substitutes.

InGaAs/InGaAsP multiple quantum well (MQW) lasers at 1.3-1.5 micron wavelength have yielded several advantages over bulk lasers at this wavelength range, such as low internal loss , high quantum efficiency, low threshold current operation and small linewidth enhancement factors [1-3]. There have been several reports predicting that further improvements are possible by employing strained layer quantum wells [4,5], as the effective mass of holes in the heavy hole sub-band of quantum well layers can be significantly reduced in the plane of the wells by compressive strain. This should result in lower threshold currents and other improvements of the laser parameters. Recently, the operation of InGaAs /InGaAsP strained layer MQW lasers at 1.5 micron was reported [6] with efficiency and output powers similar to the high values reported previously for unstrained MQW lasers. However, the expected reduction in threshold current and linewidth enhancement factor have not been observed.

The effective threshold for stimulated Brillouin scattering for a data-encoded signal is increased from 11.0 to 23.4 dBm by using a temperature-tunable laser diode. A 5 kHz sinusoid is applied to a Ti/Pt thin film resistor located along the laser contact on top of the device, resulting in a 10 kHz dithering of the wavelength. The residual amplitude modulation index at 10 kHz is only 1.2/spl times/10/sup -4/.