Jong Sool Jeong

Widely tunable dual-wavelength Er 3+ -doped fiber laser for tunable continuous-wave terahertz radiation

We propose a widely tunable dual-wavelength Erbium-doped fiber laser that uses two micro-heater-integrated Fabry-Perot laser diodes (FP-LDs) and two fiber Bragg gratings (FBGs) for tunable continuous-wave (CW) terahertz (THz) radiation. Each wavelength can be independently tuned by using an FP-LD and an FBG. The wavelength fine tuning is achieved by simultaneously applying current to the micro-heater on the FP-LD and strain to the FBG. The side-mode suppression ratio is more than 35 dB for both wavelengths. The wavelength spacing of the dual wavelength can be continuously tuned from 3.2 nm to 9.6 nm. Continuous frequency tuning of the CW THz radiation is also successfully achieved using an InGaAs-based photomixer with our dual-wavelength fiber laser as the optical beat source. The emitted CW THz radiation is continuously tuned from 0.3 to 0.8 THz.

1.25-Gb/s Operation at 50-GHz Channel Spacing Based on Intensity Noise Suppression of Wavelength-Locked Fabry–PÉrot Laser Diode

We demonstrate 1.25-Gb/s operation at 50-GHz channel spacing and 10-km single-mode fiber, which is based on a wavelength-locked Fabry-Perot laser diode (F-P LD) and an intensity noise suppression by a gain saturation of F-P LD in front of the receiver. The wavelength-locked F-P LD employs the spectrum-sliced incoherent light with narrow bandwidth of 35 GHz. The intensity noise of wavelength-locked F-P LD is suppressed about 6 dB by the F-P LD in the front of the receiver. As a result, the bit-error-rate curves exhibit the error-free performances over the detuning conditions to cover a whole mode spacing period of F-P LD.

10-Gb/s direct modulation of polymer-based tunable external cavity lasers

We demonstrate a directly-modulated 10-Gb/s tunable external cavity laser with a polymer Bragg reflector and a high speed superluminescent diode. 20 km transmission through the standard single mode fiber was carried out with a power penalty of less than 2.8 dB..

Mitigation of Rayleigh crosstalk using noise suppression technique in 10-Gb/s REAM-SOA.

We demonstrate a mitigation of Rayleigh back-scattering (RBS) impact in 10-Gb/s reflective electroabsorption modulator monolithically integrated with semiconductor optical amplifier (REAM-SOA). The technique is based on the intensity-noise suppression of the centralized incoherent seed-light, which enables smooth evolution of deployed DWDM applications. We exhibit the power penalty of less than 1 dB at the large RBS crosstalk value of about 8 dB when the optical power of seed-light is lowered about -10 dBm.

Evaluation of Chirp Reduction in Polymer-Based Tunable External-Cavity Lasers

We evaluate the chirp reduction achievable using the detuned loading effect in the polymer-based tunable externalcavity laser (ECL) capable of operating at 10 Gb/s. In particular, we estimate the achievable linewidth enhancement factor (LEF) of this ECL considering the stable operation region increased by the nonlinear gain. The results show that, due to the nonlinear gain, we can detune the lasing mode further away from the nominal detuning limit (i.e., half of the mode spacing) by ~4 GHz for an ECL with a mode spacing of ~30 GHz under the continuous-wave (CW) operating condition. As a result of this additional detuning, the effective LEF is reduced from 1.3 to 0.8, although its material LEF is ~5. However, when we change the operating wavelength of this ECL, the minimum achievable LEF is deteriorated due to the parasitic reflection occurring at the antireflection (AR)-coated facet. For example, when the optical power reflected at the AR-coated facet is ~5% of the feedback power from the polymer Bragg grating reflector (PBR), the effective LEF is increased from 0.8 to 3.4. To verify these results experimentally, we fabricate a polymerbased tunable ECL and measure its chirp characteristics. For example, we directly modulate this ECL at 10 Gb/s and measure its effective LEF as a function of the detuned frequency. The result shows that we can reduce the effective LEF to ~1 by detuning the operating mode by 18 GHz. This value is slightly larger than that achievable under the nearly CW operating condition (i.e., 0.8) due to the chirp-induced mode hopping. We also confirm that, by optimizing the detuning condition, this ECL can be used for the transmission of a 10-Gb/s signal over 20 km of a standard single-mode fiber (SSMF) with a power penalty of <;2 dB. However, an error-free transmission cannot be achieved at some wavelengths due to the parasitic reflection. To avoid this problem, it is needed to suppress the parasitic reflection to be <;0.1% of the feedback power from the PBR.

1.25-Gb/s Operation of a Spectrum-Sliced Fabry–PÉrot Laser Diode With Intensity Noise Suppression by a Second Fabry–PÉrot Laser Diode

We propose a low-cost solution for the intensity noise suppression in the spectrum-sliced Fabry-Perot laser diode (F-P LD), which is achieved by placing an F-P LD at the receiver region. The F-P LD at the receiver region provides the intensity noise suppression of about 10 dB as well as the increase of the received optical power for the spectrum-sliced optical signal. The Q-factor is improved about 5.9 at a data rate of 1.25 Gb/s. As a result, we successfully demonstrate 10-km error-free transmission at 1.25-Gb/s signal with a transmission penalty of less than 0.5 dB. It is also found that the low spectrum-sliced power of -22 dBm achieves the relative intensity noise level of -112.5 dB/Hz, which is almost independent of the operation current.

Design and performance of 10-Gb/s L-band REAM-SOA for OLT Transmitter in next generation access networks

We present a 10-Gb/s L-band reflective electro-absorption modulator integrated with a semiconductor optical amplifier (REAM-SOA) having improved transmission performance at very low input power of seed light. To decrease the input power of seed light, the absorption characteristics of the REAM are adjusted to reduce the amplified spontaneous emission light returned into the SOA, suppressing the gain saturation effect of the SOA. At a considerably low input power of -16 dBm, the REAM-SOA exhibits a low transmission penalty of about 1.2 dB after 50-km SMF transmission. Over a wide input power range from -16 dBm to 5 dBm, a penalty of less than 1.6 dB is achieved at 50-km transmission.

Simple detuning method for low-chirp operation in polymer-based tunable external-cavity lasers

We propose and demonstrate a simple detuning method for the low-chirp operation of a polymer-based tunable external-cavity laser (ECL). To ensure the low-chirp operation of this directly-modulated ECL, we first obtain the optimum values of the heater current applied to the polymer Bragg grating reflector (PBR) and the operating temperature of this ECL. For this purpose, we sweep the current applied to the phase control heater until the peak output power measured from the high-reflection (HR) coated facet reaches the minimum value. We then operate this ECL with minimum chirp by tuning the lasing mode to the longer wavelength limit of the stable operation region. This is because the detuned loading effect is maximized at this limit as the in-phase condition between the lights reflected from the PBR and anti-reflection (AR) coated facet of the gain medium is satisfied. Thus, by using this method together with conventional wavelength-locking algorithm, we can operate this ECL with minimum chirp at any wavelength.

Measurement of Facet Reflectivity Through Reflection Gain in Fabry–PÉrot Laser Diode

We propose a simple and useful method to measure the facet reflectivity in a Fabry-Perot laser diode (LD). The new measurement method does not require information on LD parameters such as threshold current or optical spectrum. The measurement is based on a simple formula that describes the relationship of facet reflectivity and reflection gain with launching the probe beam of a narrow spectral width.

Optical devices integrated with semiconductor optical amplifier

Semiconductor optical amplifiers have been used as key optical components for high capacity communication systems. Monolithic integration is necessary for the stable operation of these devices and for wider applications. In this paper, the coupling technique between different waveguides was discussed and research results about optical devices integrated with SOAs were presented. In particular laser amplifier gate switch arrays have been discussed.