K.-Y. Liou

Reduction of optical beat interference in a subcarrier multiple-access passive optical network through the use of an amplified light-emitting diode

We show that a transmitter consisting of a light-emitting diode (LED) followed by a semiconductor amplifier can be used to transmit data in a subcarrier multiple access system for fiber-in-the-loop. Optical beat interference penalties, which have been observed when conventional laser transmitters are used, were eliminated with the amplified LED. Penalty-free system operation is observed when a signal is transmitted with 17 dB less optical power than each of two interfering transmitters.

Multiple-quantum-well GaInAs/GaInAsP tapered broad-area amplifiers with monolithically integrated waveguide lens for high-power applications

A 1.48- mu m tapered broad-area semiconductor laser amplifier with a monolithically integrated waveguide lens as demonstrated. The gain saturation characteristics of the tapered amplifier were examined. A maximum output power of 300 mW and a 3-dB saturation power of 200 mW under quasi-CW conditions were obtained from the amplifier without the waveguide lens. Output power of 200 mW was obtained with a broad emission spectrum of approximately 30 nm when the device was used as a superluminescent diode. The amplified output was focused to a single lobe by the monolithically integrated aspheric waveguide lens, which may be useful for efficient coupling of the output into a single-mode fiber.<<ETX>>

A 5 Gb/s monolithically integrated lightwave transmitter with 1.5 mu m multiple quantum well laser and HBT driver circuit

A multiple quantum well ridge waveguide laser at 1.5- mu m wavelength and a driver circuit comprised of four heterojunction bipolar transistors (HBTs) have been monolithically integrated on a semiinsulating InP substrate. This optoelectronic integrated circuit (OEIC) has been realized by metalorganic vapor phase epitaxy. The laser threshold current is near 20 mA. The HBT DC current gain is 40 and the unity gain cutoff frequency is 30 GHz. Pseudorandom pulsed operation of the OEIC transmitter has been demonstrated for bit rates up to 5 Gb/s.<<ETX>>

Operation of an LED with a single-mode semiconductor amplifier as a broad-band 1.3-μm transmitter source

A semiconductor amplifier and an edge-emitting LED are operated in a single-mode-fiber connected configuration to demonstrate a broad-linewidth 1.3-/spl mu/m transmitter. The output from the LED is increased by a 13.5-dB chip gain through the amplifier to 2.3-mW while maintaining a broad 3-dB spectral width of 600 /spl Aring/ from the LED. A 600-Mb/s modulation speed was demonstrated, with open eye-patterns from the amplifier, with direct current modulation applied to the LED. A theoretical analysis shows that the LED-amplifier gain is about 7 dB less than the peak amplifier gain for a narrow-line signal due to the broad spectrum and wavelength offset of the LED. The 1.3-/spl mu/m LED-amplifier may be useful as a transmitter for fiber access networks to avoid optical beat interference noise, or as a broadband source for wavelength sliced WDM networks. The device has the potential to be monolithically integrated for wavelengths at 1.3 and 1.5 /spl mu/m.<<ETX>>

Linewidth‐narrowed distributed feedback injection lasers with long cavity length and detuned Bragg wavelength

We report linewidth narrowing for 1.3‐μm InGaAsP distributed feedback lasers with either a long cavity length or a detuned Bragg wavelength. The narrowest linewidth measured was 3 MHz at 6 mW for a 780‐μm long‐cavity laser, and was 8 MHz at 5.5 mW for a 250‐μm regular‐length laser with detuned wavelength. From our analysis, distributed feedback lasers with 1 MHz linewidth appear to be feasible.

A WDM access system architecture based on spectral slicing of an amplified LED and delay-line multiplexing and encoding of eight wavelength channels for 64 subscribers

We propose and demonstrate a novel spectrum-sliced and delay-line multiplexed multiple-wavelength source and its use in a WDM access system. In the proposed system, the pulsed output from an amplified LED is spectrally sliced by a WDM router and multiplexed with short fiber delay lines into individually addressable wavelength channels that can be modulated with an external modulator. By using an Er-fiber amplified 1.55-/spl mu/m LED as the source, eight-channel WDM routers, an 8/spl times/8 star coupler, and monolithically integrated amplifier-modulator chips for data encoding, our experiment demonstrated that a single LED can provide down-stream WDM links to 64 subscribers each at 50 Mb/s.

Monolithically integrated semiconductor LED-amplifier for applications as transceivers in fiber access systems

We have fabricated a monolithically integrated LED-amplifier chip for application as a high-power broad-band transmitter. Amplified LED output of 10 mW and fiber-coupled power of 4 mW was demonstrated. The device can be used as a spectrally-sliced transmitter for wavelength-division-multiplexed networks or as a broad-band transmitter in subcarrier multiple-access systems to eliminate optical beat interference. The amplifier section in the integrated device can also be used as a photodetector. The performance of the device as a transceiver in a WDM multiple-access system operating at a typically proposed local-access data rate of 10 Mb/s was successfully demonstrated.

Single‐longitudinal‐mode stabilized graded‐index‐rod external coupled‐cavity laser

An active‐passive coupled‐cavity semiconductor laser using a slightly shorter than 1/4 pitch graded‐index‐rod lens reflector as the external cavity has been demonstrated. The graded‐index lens is prepared from an optical fiber waveguide. We report (1) stable single‐longitudinal‐mode operation of the graded‐index‐rod external coupled‐cavity (GRECC) lasers with 2‐Gbits/s modulation and (2) digital transmission at 1 Gbits/s over 99 km of fiber using a 1.55‐μm GRECC laser.

Linewidth characteristics of fiber‐extended‐cavity distributed‐feedback lasers

A 1.55‐μm wavelength InGaAsP distributed feedback (DFB) laser with an antireflection coated facet has been coupled to a single‐mode fiber with a reflective end to construct a compact narrow‐linewidth source. The linewidth of the DFB laser is reduced by a factor of 1000 to 70 kHz at 1 mW output with a 5.5‐cm fiber length. The fiber mirror to DFB laser coupling parameters required for narrow‐linewidth operation are presented.

A 24-channel wavelength-selectable Er-fiber ring laser with intracavity waveguide-grating-router and semiconductor Fabry-Perot filter

We present an Er-doped fiber ring laser that operates with a single wavelength, which is selectable from any channel wavelength of a 24-channel silica waveguide grating router. A semiconductor Fabry-Perot optical amplifier is used as an intracavity narrow-band filter to stabilize laser oscillation in a single axial mode. We show by experiment and a theoretical model that the long cavity mode buildup time of the Er-fiber laser and multiple passes through the intracavity filter can effectively stabilize the laser output in a single mode. An electroabsorption modulator is used to modulate the laser output at a selected wavelength. Error-free performance is demonstrated, we believe for the first time, for a waveguide grating router fiber laser at 5 Gb/s.