Traveling-wave Semiconductor Optical Amplifier Research Articles

50 km bidirectional FTTH transmission comparing different PON standards

In this paper, a bidirectional Fiber To The Home (FTTH) is proposed where WDM transmitter is used as a seeding source with wavelength of 1550nm. The system utilizes a Travelling wave Semiconductor Optical Amplifier (TSOA) with injection current 0.15A. 50km range FTTH architecture is demonstrated for both downstream and upstream channels. We investigated the impact of different data rates on upstream and downstream data. The BER results show that the performance of our scheme is good for 10Gbps system for downstream transmission as it accommodates 64 ONUs. From simulation results show the BER of 9.95e-009 is reported at 15Gbps but only in case of 32 ONUs. Similarly, in case of upstream transmission, Q-Factor of 15.04dB is reported for 32 ONUs. So this scheme is a practical solution to meet the data rate of the optical links simultaneously in tomorrow's PON access networks.

An efficient electrode arrangement for TWSOA based inline detector

An efficient electrode scheme is developed to enhance the inline detector performance of a 1.55μm, InP–InGaAsP, Traveling Wave-Semiconductor Optical Amplifier (TW-SOA). A traveling wave approach is used to determine the voltage developed along the length of the TWSOA, accurately. A single electrode along the entire length of the device and a single, short length electrode kept at certain distance from the front facet are investigated, for input optical power levels ranging from −25dBm to +5dBm. Efficient position of the single electrode along the cavity length is determined for maximum detected voltage. Under this scheme, the inline detector with an electrode length of 100μm positioned at 200μm from the front facet, is found to provide a improvement of 6dB and 8dB in detected voltage for 40mA and 50mA bias respectively, at −10dBm input, when compared with the maximum detected voltage reported in the literature.

Numerical Analysis of NTW-SOA for Differential Inline Detector Applications

An analysis of Near Travelling Wave-Semiconductor Optical Amplifier (NTW-SOA) is presented to investigate its inline detector performance. The detected voltage is evaluated for various lengths and positions of the electrode along the active region of the device, for input optical power levels ranging from −25; dBm to +5 dBm. Under optimum conditions, the differential detection scheme shows an improvement of 3.7 dB, 4 dB for 40 mA, 50 mA bias currents respectively at −10 dBm input power, when compared with the best differential inline detection scheme reported in the literature. Further an improvement of 4.3 dB and 5.5 dB are obtained, when compared with the single electrode detection model under similar operating conditions.

Broadband semiconductor optical amplifiers of the spectral range

A line of travelling-wave semiconductor optical amplifiers (SOAs) based on heterostructures used for production of broadband superluminescent diodes is developed. The pure small-signal gains of the developed SOA modules are about , while the gain bandwidths at a level of reach . As a whole, the SOA modules cover the IR spectral range from 750 to . The SOAs demonstrate a high reliability at a single-mode fibre-coupled cw output power up to . Examples of application of two of the developed SOA modules as active elements of broadband fast-tunable lasers are presented.

All-Optical Phase Control of a Square-Wave Photonic Clock

We propose and demonstrate an all-optical technique to control the phase of a class of square-wave photonic clocks. The particular photonic clock used for our demonstration is comprised of a traveling-wave semiconductor optical amplifier (SOA) connected to a resonant-type SOA exhibiting hysteresis. Phase control is achieved by cross-gain modulation within the travelling-wave (TW)-SOA, which suspends clock generation over a controlled time interval to achieve the desired phase. We used 1576-nm control pulses with 62- μW peak power and arbitrary polarization states, features that are telecommunications compatible. A useful feature of our scheme is that phase control is independent of the synchronization between the initial clock phase and arrival time of the control pulse.

Optical Square-Wave Clock Generation Based on an All-Optical Flip-Flop

We demonstrate optical square-wave clock generation based on an all-optical flip-flop. The bistable output power from a resonant-type semiconductor optical amplifier (SOA) is switched on and off by modulating its input with its output via cross-gain modulation in a traveling-wave SOA. All active components are driven by dc currents, and the wavelength and clock frequency are selectable. A clock frequency of 3.5 MHz is demonstrated, limited by the time of flight between bulk optical components. Optical square-wave clock signals are promising for applications in photonic integrated circuits and all-optical signal processing.

Circuit model for analysis of SOA-based photonic switch

This paper presents an equivalent lumped element electric circuit model for traveling wave semiconductor optical amplifier (SOA) in integrated circuit applications. The model facilitates incorporation of chip and package parasitic elements of SOA. The model is used to represent an all optical 2 × 2 switch based on cross gain modulation in SOA capable of operating at an ultra fast speed. SPICE simulation of the switch with the proposed circuit model provides bit error rate (BER) values at the switch output which agrees well with the experimentally measured values at 10 Gb/s. The degradation of switching performance has been examined in terms of bit error rate, modulation bandwidth and switching time in the presence of chip parasitic elements of SOA.

All-Optical RZ Data Conversion With Temporally and Spectrally Gain-Sliced Semiconductor Optical Amplifier Via Broadband Optical Injection

We investigate the effect of the backward injecting linewidth on the rise/fall time, duty cycle, and frequency chirp of the 10 Gb/s format-converted pulsed return-to-zero (RZ) data stream from the traveling-wave semiconductor optical amplifier (TWSOA) with its gain profile temporally and spectrally reshaping by a backward injected single- or multimode inverse-optical-comb. The rising time remains almost unchanged; however, the falling time was monotonically reduced by increasing injection power. The evolution of full-width at half-maximum with injection power exhibits similar trend with falling time. In comparison with single-mode inverse-optical-comb injection, the multimode injection exhibits frequency-chirp reduction and better on/off extinction performances. Under the injection of multi- and single-mode inverse-optical-combs into the TWSOA at extremely high gain condition, the multi- and single-mode injection converted pulsed RZ data pulsewidths are 32 and 31 ps with corresponding peak-to-peak chirps of 10 and 12 GHz, respectively. The chirp can abruptly be reduced to 1.2 GHz by reducing the TWSOA biased current to 100 mA.

Dynamic chirp control of all-optical format-converted pulsed data from a multi-wavelength inverse-optical-comb injected semiconductor optical amplifier

By spectrally and temporally reshaping the gain-window of a traveling-wave semiconductor optical amplifier (TWSOA) with a backward injected multi- or single-wavelength inverse-optical-comb, we theoretically and experimentally investigate the dynamic frequency chirp of the all-optical 10GBit/s Return-to-Zero (RZ) data-stream format-converted from the TWSOA under strong cross-gain depletion scheme. The multi-wavelength inverse-optical-comb injection effectively depletes the TWSOA gain spectrally and temporally, remaining a narrow gain-window and a reduced spectral linewidth and provide a converted RZ data with a smaller peak-to-peak frequency chirp of 6.7 GHz. Even at high inverse-optical-comb injection power and highly biased current condition for improving the operational bit-rate, the chirp of the multi-wavelength-injection converted RZ pulse is still 2.1-GHz smaller than that obtained by using single-wavelength injection at a cost of slight pulse-width broadening by 1 ps.

Optical Bistability in a Traveling-Wave SOA Connected to a DFB Laser Diode: Theory and Experiment

We investigate the bistable response of a traveling-wave semiconductor optical amplifier (SOA) connected bidirectionally to a distributed feedback (DFB) laser diode. By contrast to dispersive DFB amplifiers, bistability is possible for a broad wavelength range of the injected optical signal. A theoretical analysis clarifies the origin of the phenomenon and the conditions under which it occurs. Numerical simulations and experimental results confirm the theoretical analysis. Experimentally obtained step heights up to 25 dB and widths of the bistability domain of 1-4 dB have been found

110-pJ and 410-fs pulse at 10 GHz generated by single-stage external fiber compression of optically injection-mode-locked semiconductor optical amplifier fiber laser

We demonstrate the high-power amplification and single-stage fiber-based pulse compression of a traveling-wave semiconductor optical amplifier (TWSOA) fiber ring laser (SOAFL), which is optically mode-locked by backward injecting the TWSOA with a dark-optical-comb at repetition frequency of 10 GHz. A negatively chirped SOAFL pulsewidth of 5.4 ps is compensated and shortened to 3.9 ps by a 75-m-long dispersion compensating fiber. With a single-stage pulse compression in a single-mode-fiber spool, the SOAFL pulses with input average power of 1.7 W can further be compressed to a pulsewidth of 410 fs, corresponding to a pulse compressing ratio of nearly ten. The maximum average output power of the amplified SOAFL pulse is up to 1.1 W, corresponding to the peak power and pulse energy of >0.27 kW and 110 pJ, respectively.

Characteristics measurement of gain and refractive index of traveling-wave semiconductor optical amplifier

A novel method to measure the gain and refractive index characteristics of traveling-wave semiconductor optical amplifier (TMA) is presented. In-out fiber ends of TWA are used to construct an external cavity resonator to produce big ripple on amplified spontaneous emission (ASE) spectrum. By this means, Hakki-Paoll method is adopted to obtain the gain spectra of TWA over a wide spectral range. From measured longitudinal mode spacing and peak wavelength shift due to increased bias current, we further calculate the effective refractive index and the refractive index change. Special feature of refractive index change above lasing threshold is revealed and explained.

Broadband highly bright radiation sources based on a superluminescent diode and a semiconductor optical amplifier

It is shown experimentally that the use of a travelling-wave semiconductor optical amplifier (SOA) significantly improves the output characteristics of a superluminescent diode (SLD), increasing, in particular, its output power or broadening its emission band. By using SOAs based on separate-confinement double (InGa)PAs heterostructures emitting at 1300 nm and different SLDs as input radiation sources, there were obtained up to 50 mW of cw power at the output of a single-mode fibre and the emission band with the half-width up to 70 nm.

Spectral characteristics of a regenerative semiconductor optical amplifier mutually injection locked with a Fabry-Perot laser diode.

The anomalous injection locking of a traveling-wave semiconductor optical amplifier (SOA) and a fiber-pigtailed Fabry-Perot laser diode (FPLD) linked with single-mode and improved side-mode suppression ratio output is demonstrated. We achieve this injection locking by driving the FPLD slightly below threshold and by feedback injecting the FPLD with fractional output of a closed-loop SOA. The SOA-FPLD link lases in a single FPLD longitudinal mode with a reduced linewidth of 0.013 nm and a maximum side-mode-suppressing ratio of 39.7 dB. A precise 3-dB linewidth of 45-50 MHz is also observed from the self-homodyne mode-beating spectrum. The optimized feedback-injecting power for the FPLD is approximately 2% of the SOA-FPLD linked output power of >400 microW. The variations in output power and in peak wavelength are not more than 0.54% and 0.06%, respectively. The injection-locked SOA-FPLD link is insensitive to the temperature fluctuation within +/- 0.25 degrees C.

Gain dynamics of semiconductor optical amplifiers and three-wavelength devices

A numerical model that accounts for the effects of the amplified spontaneous emission (ASE) on the carrier dynamics in a travelling wave semiconductor optical amplifier is presented. The ASE is modeled using effective parameters that are derived starting from the spontaneous emission and gain models. The gain dynamics are then analyzed using the parameters extracted from measurements on a real device to explain the overshoot in the gain recovery. The model is also used to simulate the gain recovery in a three-wavelength device configuration for various injected powers and wavelengths. The recovery time when the injected beam is at the device transparency wavelength is also analyzed with particular attention to the differences between co- and counter-propagating configurations.

Two-segment spectrally inhomogeneous traveling wave semiconductor optical amplifiers applied to spectral equalization

Spectral equalization devices for an optical analog-to-digital (A-to-D) converting system have been theoretically analyzed and fabricated. Selective area growth was used to define a multiple-section active region. Two-segment semiconductor optical amplifier with current adjustable gain spectrum is demonstrated.

Picosecond chirped‐pulse amplification in traveling‐wave semiconductor optical amplifiers

AbstractThe characteristics of traveling‐wave semiconductor optical amplifiers (TWSOAs) used for the picosecond pulse amplification process are discussed. The distortion of a multigigabit chirped optical pulse train generated from gain‐switched optical transmitters due to a saturation of output power and a gain of TWSOAs is analyzed. The optimized injection current and operating temperature of TWSOAs in amplification of picosecond negatively chirped optical pulses are determined. The shortest optical pulse is found to broaden from 21 ps to 30 ps after amplification by TWSOA. © 2002 Wiley Periodicals, Inc. Microwave Opt Technol Lett 33: 202–207, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.10276

Analytical Expressions of the Various Derivatives of the Output Power of the Semiconductor Optical Amplifiers with Respect to the Input Power

Based on the physical fact that the nonlinear distortions induced by the travelingwave semiconductor optical amplifiers in the subcarrier multiplexing CATV transmission system can be calculated by expressing the output power P o of the amplifiers with the Taylor series of the input optical power P i and specifying the various order derivatives of P o with respect to P i , the solutions to the rate equations of the amplifiers have been derived, and the analytical expressions of the various order derivatives of P o with respect to P i have been obtained and simulated numerically by selecting typical amplifier parameters.

Small signal analysis of frequency response of four-wave mixing in semiconductor optical amplifiers

A theory of small signal frequency response of four-wave mixing (FWM) in a traveling wave semiconductor optical amplifier has been developed. The bandwidth of FWM is >300 GHz. For large wavelength separation between the input signals, where the nonlinear gain effects dominate the generation of FWM, the bandwidth of the FWM signal exceeds 1 THz.

Polarization-independent four-wave mixing in a bidirectional traveling-wave semiconductor optical amplifier

In this work, we demonstrate polarization-independent four-wave mixing using a single semiconductor optical amplifier. The result is obtained using a polarization-diversity scheme, in which all the injected fields are split by a polarization beam splitter and the two resulting patterns are injected counterpropagating in the amplifier. The use of two orthogonally polarized pumps allows a conjugate generation with efficiency also independent of the signal-conjugate detuning. A comparison of the amplifier performance with mono- and bidirectional propagation is given.