Several commercial GaAlAs and InGaAsP injection lasers have been investigated with respect to their photodetection properties. The responsivity of the laser diode detectors is in the 0.15-0.25 A/W range and the dark current ranges from 5 nA to 500 nA at 3-V reverse bias. The high frequency performance of a laser diode detector strongly depends on the laser structure. The bandwidth is determined by the capacitance of the lasers and ranges from 70 MHz to 1.3 GHz. The structure showing the fastest response was the TJS laser due to its low junction capacitance.

Photodetection properties of semiconductor laser diode detectors

The photodetection capabilities of 1.3- mu m channel substrate lasers are studied. The diodes can be used either as lasers or detectors in single-mode-fiber half-duplex communication links. As a detector, a responsivity of 0.26 A/W is obtained by efficiently coupling the input radiation into the facet using a lensed single-mode fiber. The spectral bandwidth extends from 1.1 to 1.37 mu m. The dark current at room temperature is 200 nA at 1-V bias and due in part to current leakage through the Fe-doped InP blocking layer. As lasers, the diodes have a frequency response of 4 GHz, and as detectors, the 3-dB bandwidth is 600 MHz. >

Characteristics of 1.3- mu m InGaAsP lasers used as photodetectors

A bidirectional system using 1.3 mu m lasers as a transmitter and a receiver are investigated. The lasers considered are commercially available Fabry-Perot and distributed-feedback lasers. It is found that the poor performance of a laser receiver, compared to a PIN receiver, stems from three factors: low responsivity, high capacitance, and polarization dependence of responsivity, high capacitance, and polarization dependence of responsivity. The effect of each factor is evaluated. It has been clarified that the polarization dependence of sensitivity originates from the TE and TM modes dependence of both mode confinement factor and reflection at a facet. Using the measured parameters, 1.3- mu m laser receiver sensitivity for a 10/sup -9/ error rate is estimated. Burst data transmission experiments show that estimated sensitivities agree well with the measured values. Optical ping-pong transmission distance of narrowband services is determined based on estimated sensitivity. >

Time compression multiplex transmission system using a 1.3 mu m semiconductor laser as a transmitter and a receiver

The fabrication of a colocated three-dimensional stacked thin-film device, which can be used for single-fiber bidirectional communication, has been demonstrated. A thin-film light-emitting diode (LED) with a diameter of 50 /spl mu/m has been stacked on top of a thin-film inverted metal-semiconductor-metal (I-MSM) photodetector (PD) with a detecting diameter of 200 /spl mu/m. Both devices in the stack have been tested, and the I-MSM PD in the PD/LED stack has a responsivity of 0.31 A/W, which is consistent with the theoretical analysis using a uniform illumination approximation.

A 3-D bidirectional optical link using a stacked thin-film emitter and detector

An optical isolator for laser-to-single-mode fiber coupling is discussed. The coupling unit consists of a confocal two-lens system with a spherical glass lens and a planoconvex lens which is made of yttrium iron garnet (YIG). To minimize the number of elements, the YIG lens is used as a Faraday rotator as well as a coupling lens. Nevertheless, the planoconvex YIG lens satisfies the requirements of high coupling efficiency, high isolation, and low optical feedback from the Faraday rotator. The arrangement is theoretically and experimentally investigated. At a coupling efficiency of 34%, the total optical feedback into the laser diode was measured to be about -60 dB. >

A compact optical isolator with a plano-convex YIG lens for laser-to-fiber coupling

Semiduplex, high-data-rate transmission over a single optical fiber using GaAs/GaAlAs channeled substrate planar (CSP) structure lasers both as light source and photodetector has been demonstrated. The responsivity in the receiving mode at the operating wavelength (830 nm) was 0.15 A/W. This device is suitable for semiduplex transmission, since the emissive spot and the photosensitive area of the laser coincide. The impulse response was measured to be 2.5 ns full width at half maximum (FWHM) at zero bias voltage. A 500-m single-mode fiber was used, and by using microlenses the input coupling loss was reduced to less than 4.5 dB. Measurements at a data rate of 100 Mbit/s return to zero (RZ) shows an optical power margin of 14 dB for a bit error rate (BER) of 10-9. Using lasers instead of LED's as transceivers would improve the transmission capability and the system margin of a semiduplex communication link.

R. Tell

Papers

100-Mbit/s semiduplex optical fiber transmission experiment using GaAs/GaAlAs laser transceivers