Hyuek Jae Lee

Pulse-amplitude equalization of rational harmonic mode-locked fiber laser using a semiconductor optical amplifier loop mirror

Abstract The authors demonstrate, for the first time to our knowledge, the amplitude equalization of high-repetition-rate pulses generated from a rational harmonic mode-locked fiber laser using a semiconductor optical amplifier loop mirror. Here, the loop mirror acts as an all-optical pulse-amplitude equalizer. Optimized parameters of the loop mirror for pulse-amplitude equalization were determined by a simulation. The pulse-amplitude equalization was successfully demonstrated up to the thirteenth rational harmonic mode-locked pulse train (∼14 GHz).

Novel all-optical edge detector for the clock component extraction of NRZ signal using an SOA-loop-mirror

The authors demonstrate an all-optical edge detector for the clock component extraction of the non-return-to-zero (NRZ) signal using a semiconductor optical amplifier (SOA) loop mirror, which acts as an exclusive OR (XOR) logic gate for the input NRZ signal and its delayed signal. The extracted clock components from the edge detection for the NRZ signal at 10 Gb/s were confirmed to show the input polarization dependency of less than 1 dB.

A gain-flattened two-stage EDFA for WDM optical networks with a fast link control channel

A two-stage erbium-doped fiber amplifier (EDFA) providing constant output power and flat gain regardless of abrupt variations of the number of channels and upstream losses is designed and fabricated by controlling each stages pump power and mid-stage attenuation. The two-stage EDFAs were successfully applied in the 10 Gbit/s/channel WDM network with a fast link control channel having a 1.6 μs response time to transmit one surviving channel over a 180 km DSF when 7 out of 8 channels are added/dropped.

All-optical burst-mode clock extraction based on the thresholding operation of a modified terahertz optical asymmetric demultiplexer

Abstract To implement all-optical burst-mode clock extraction we adopt a modified terahertz optical asymmetric demultiplexer (MTOAD). The transmittance and reflectance of the MTOAD depend on the input intensity. For the MTOAD, two levels of pulse intensity can be chosen in such a way that while the pulses with similar intensity are reflected for both strong and weak pulses, only the strong pulse transmits. The device is useful, for example, for bit-level clock extraction from a packet, where strong and weak intensity pulses are assigned to `1 and `0, respectively. When the input optical signal power is fixed to −1.6 dBm and the intensity ratio between `1 and `0 is varied in the range of 0.2–0.5, the extinction ratio (ER) at the transmitted port is more than 10 dB and a clock amplitude jitter (CAJ) of the bit-level clock at the reflected port is less than 14%. Inversely, when the input power is varied in the range of −6–−1 dBm with fixed intensity ratio of 0.3, more than 11 dB of ER and less than 15% of CAJ are obtained.

Efficient 3N-optical pulse generator based on multistage fiber loop mirror

Abstract We propose a novel power efficient multistage fiber loop mirror pulse generator (FLMPG) scheme which transforms a single optical pulse into 3N optical pulses. While a conventional parallel scheme loses 2/3 of total power to convert an optical pulse into three optical pulses, our scheme loses only 2/5 of total power, improving the efficiency 1.8 times. The 3N optical pulse generator combined with the well-known ladder scheme 2N optical pulse generator can provide more flexibility for generating an arbitrary number of optical pulses. Two-stage and three-stage fiber loop mirror pulse generators are analyzed theoretically by the Jones matrix method. In addition, we have successfully realized two-stage and three-stage FLMPGs which generate three and nine pulses out of one pulse, respectively.

Nonlinear optical moiety-doped polymers with improved optical properties for photonic devices

An electro-optic polymer guest-host system has been constructed and demonstrated. The polymer host is a polyimide (PIQ2200) and the guest chromophores are dimethyl (or diethyl) amino alkyl sulfone stilbenes. The alkylated-NLO moieties as guest chromophores have been modified, yielding new alkylated-NLO moieties. The higher content of alkylated-NLO moieties, compared to unmodified NLO moieties, was doped into a polyimide host system due to the improved solubility of new alkylated-NLO moieties. To the 40 wt%, the new alkylated- NLO moiety has been completely dissolved in the preliminary experiment, leading to the increase of refractive index by 0.0016. These polyimide-based guest-host systems exhibited a significant improvement in the thermal stability at high temperatures exceeding 250 degree(s)C. The electro-optic coefficient reported in the present study is 13 pm/V for the 40 wt% DASS-6- doped polymer system poled at the 135 V/micrometers . However, further increase up to 25 pm/V may easily be achieved by increasing the amount of guest moieties and/or the intensity of the poling field. This work presents new materials for photonic switching devices with low operating voltage.

Modified Terahertz Optical Asymmetric Demultiplexer for the Extinction Ratio Enhancement of All-Optical NRZ-to-Inverted-RZ Converter

In fume all-apiical ocrwaks, it is llxely thaf both WDM and CrTDM will be inmrpaaled. m d thas will be B ned far all-optical dats f m a t mvsJidrrumvaJim h e m WDM and OTDM [ I]. N m m ~ . * u r o (NRZ) mdrc lum-I -m(RZ) formatrarrmonlyuvdPmongsv~ietyofdaufmnstr.NRZfam~1 harthcmsitoflaua bandwidth rquvmenl and highs timing jina ldmce than R2 f m s t , wllile RZ fmnai is prcfard io ulmfsst OTDM ndwakr to make use of bit-mlalsuing ishniquc. Some p r d ~ rarks haw denanmated NRZ-t(inmd>RZ mwas using nonlinear optical Imp m i r r a (NOLM) m d moss-gain com-im of mniunduEtoropticalamplifio(SOA)Ill.NRZl~inverVbRZmnvmnbavdonaos3-gainmmprarianofSOA has lhemmi ofsimplicity in mnnrmefim, th& icI enindim n l i a (ER) is p m To impER, ws have perislly ddd a modified I dSnr optical ssymmmk dmultiplcxer (TOAD) [2] 10 L e mvcner. ln Lis pp, we p r q w and demmglrare ERmhmcsdNRZt-invsned-RZ MVCMI Expaimmul UNP i s show in Fig. I. @tical NRZ signal is g m d by dim mcdularim of 1311 nm DFB.LDI -tin8 at the speed of 2 GbiWr and synchronized 2 G% optical clotk i6 gmated by u h g gain. witching of 1305 nm DFB-LD2. ?%e clmica1 signals to g m s r e thee optieel signals m e obtaind frcan a pulse potmc 8mmalor ( P P O ) . A fixed dilCnwml wupla (FE€) m b i n c s ihac lw opical rignslr and smdr f h m U) SOAI. ?%e converted F Z signal of 1305 nm wYclcngth by cro~-gain mmprasim 11 SOAI io e x w e d lhrwgh the optical band pasr filter IBPFI 1. I1 i s worth nning that the r e u l m t R2 signal i s invmd with rerpa to the original NR2 signd. Exiina%on rslie (ER) of the NWA-invertcd-RZ W Y n f a bavd m SOA =--gain umprs5im is w P, Wically lei than 8 dB. To improve ER Ule mvmed-RZ signal MS incidmt U) a modified TOAD The mmitImce ofTOAD can be sdjurted in such a way that the urak signal flanmimnce is maller than the Srmg simal cMSmitl8oce. The dasilr ofthc apnatlmal principle ofthc modified TOAD CM k I m d h Ref. 121. me sign& were detected by B m m m l ~ ~ i a l lightwave &eclor and k e d by B digitizing a c i l l ~ (DOSC). The optical p r ofthr input NRZ signal varied %om I2 d8m to -2.26 dBm with ERrange 2.7 dB 7.4 dB as &own in Fig. 2. 111w11ed-U signal by mowgain mmpmim of SO A I monitarcd st pin1 A in Fig. I. T h e ER ofthe inwed-RZ Iiwal varied widely depending m the q t l c a l p ~ v e r of input NRZ data, giving ER range of 1.6-6.7 dL. As i s cxpned ER ofthe input si& haeared whm the optical power wah l n a r a w d s n d t h c N R Z ~ i . i n v ~ I V m o n m . d e I dBdcgsdsfionofER.ThcERmh~nsedRZsignalby the mdificd TOAD w darned aI win1 8 in Fig. I. when the invmed-U signal p a s 4 l h W TOAD, ER ~impravedto5 .4-14 .5dRupto10.4dBimprovancnIbantheinpuINHZ~lgnnal .Vsryi~t~~t ingl~ ,~ef inal inwed-RZ signal showed input p w c ~ indspcndmi ER, i.e. 14.5 dB fa the inwt p ~ v e r m g c -6 -2 a m . This L n p l i e t h s t B e p r ~ ~ ~ h e m c m a y p l a y a n ~ l i a l m l e i n h~ndlingopficalrignalrofwidrrangcintcnsity. that -I meviuhle in real--Id all-apt~cll n-k. The pm~sd NRZ.1~lnvutcd-RZ m v e r t n offm v e y large dynamic mvming mge fa the input oplml pow, and will pave U a kcy block fm all-optical WDM and