A wavelength division multiplexing (WDM) unit for single-mode fiber (SMF) duplex transmission, with light source, photodiode (PD), and WDM coupler arranged on a common substrate, is described. Using a tolerant optical design, the optical elements, e.g. lenses and fibers, are positioned in embossed high-precision V grooves without active adjustments. Only the light source, a laser diode (LD) or an edge-emitting LED (ELED), must be aligned for optimum coupling and fixed by laser welding. Typical values of LD-to-fiber and fiber-to-PD coupling loss and crosstalk are 5 dB, 1.2 dB, and -44 dB, respectively. Hence, in spite of the potentially low-cost design, the optical performance of the device is virtually competitive with separated transmitter and receiver units.

The attractiveness of LEDs and single-mode fibers (SMFs) for application in subscriber loop networks is well known. So far primarily 1.3- and 1.5-μm edge-emitting LEDs have been used for bidirectional WDM transmission.1,2 This paper describes transmission experiments employing 1.17- and 1.3-μm LEDs at 140 Mbit/s. Compared with 1.5 μm the shorter wavelength LEDs have the advantages of a higher coupled power into SMFs and a considerable narrower spectral width causing smaller dispersion penalties.

For the first time a light power exceeding 100 μW has been coupled into a single-mode fibre from an edge-emitting diode at a current less than 100 mA. The design and properties of the diodes are described in the letter.

Fabrication et optimisation de ces diodes pour obtenir un maximum de puissance couplee dans une fibre optique a gradient d'indice

Bereits auf der Laser 79 wurde über Aufbau und Eigenschaften des V-Nut- Lasers berichtet [l]. Bevor im folgenden auf neuere Ergebnisse bezüglich Lebensdauer und hohen Pulsausgangsleistungen im einzelnen eingegangen wird, soll die in Fig. 1 dargestellte Struktur nochmals kurz beschrieben werden. Sie unterscheidet sich von einer normalen Doppelheterostruktur, indem die obere p-dotierte GaAlAs-Mantelschicht durch zwei Schichten ersetzt wird, die p- und n-dotiert sind. Der dadurch zusätzlich entstehende in Sperrichtung vorgespannte pn-Übergang ist nur in dem schmalen Bereich leitend, der unmittelbar unter der durch Ätzen hergestellten V-Nut von der Zn-Diffusionsfront durchstoßen wird. Auf diese einfache Weise lassen sich Streifenlaser mit Streifenbreiten von 4–6 μm herstellen, die im kontinuierlichen Betrieb bis zu Ausgangsleistungen von 50 mW/Spiegel kinkfrei sind. Anwendungen in der Fasermeßtechnik geeignet.

For designingV-groove lasers, the influence of the width of current injectionwand the distancedof the diffusion front from the active layer is considered. Two laser designs with stable emission properties have been found: the first possibility consists of using a narrow current injection (w \approx 3 \mum) while, alternatively, a wider current injection (w \approx 5...8 \mum) can be used ifdis les...

GalnAsP/InP double-heterostructure lasers were grown by liquid-phase epitaxy on (100) InP substrates for the wavelength region around 1.3 μm. The preparation and the properties of the wafers are described in detail. The characterisation includes the determination of the band-gap energy, the lattice mismatch of the GalnAsP active layer to InP as a function of the melt composition, and the measurement of the optical-gain spectra. Oxide-stripe geometry lasers, prepared from the wafers, lase at around 1.3 μm with pulsed thresholds between 300 and 400 mA. Some samples have been tested in c.w. operation at room temperature for more than 1400 hours. During the first 1000 hours a threshold increase of typically 2% has been observed.

Various optical output characteristics of double-heterostructure lasers have been examined, together with the response of laser emission current pulses. Correlations between the two have been observed.