Bh Verbeek

Planar monomode optical couplers based on multimode interference effects

The self-imaging property of a homogeneous multimoded planar optical waveguide has been applied in the design of passive planar monomode optical couplers based on multimode interference (MMI). Based on these designs, 3 dB and cross couplers were fabricated in SiO/sub 2//Al/sub 2/O/sub 3//SiO/sub 2/ channel waveguides on Si substrates. Theoretical predictions and experimental results at 1.52- mu m wavelength are presented which demonstrate that MMI couplers offer high performance: on-chip excess loss better than 0.5 dB, high reproducibility, low polarization dependence and small device size. >

Mach-Zehnder interferometer polarization splitter in InGaAsP/InP

A passive TE/TM mode polarization splitter based on a Mach-Zehnder interferometer is demonstrated. Insertion loss of 1.5 db and extinction ratios of /spl minus/19 dB for TE and /spl minus/15 dB for TM have been measured at 1510-nm wavelength. The device attains large optical bandwidth employing a pair of multimode interference (MMI) couplers and a wavelength-tolerant birefringent structure.<<ETX>>

Low-loss phased-array based 4-channel wavelength demultiplexer integrated with photodetectors

A 4-channel phased-array wavelength division demultiplexer with 1.8 nm channel spacing at 1.54 /spl mu/m has been monolithically integrated with photodetectors in InP/InGaAsP. On chip losses are 3.5 to 4.5 dB. These are the lowest losses reported so far for demultiplexers monolithically integrated with photodetectors. Nearest neighbor crosstalk ranges from /spl minus/12 to /spl minus/21 dB.<<ETX>>

A compact nine-channel multiwavelength laser

A phased-array-based multiwavelength laser has been realized on a chip area of 3.5/spl times/2.5 mm/sup 2/. The device has nine channels, spaced at 400 GHz around a central wavelength of 1.55 /spl mu/m. Its performance is characterized by a minimum threshold current of 101 mA, a maximum fiber-coupled power of 0.37 mW, and a linewidth of 21 MHz. In addition, simultaneous four-channel operation is demonstrated.

An optical passive 3-dB TMI-coupler with reduced fabrication tolerance sensitivity

Two-mode-interference (TM) couplers are shorter than weakly coupled waveguides, and less sensitive to production tolerances. Modifications for further reduction of the sensitivity of the coupler to production tolerances are presented and experimentally demonstrated. 3-dB couplers with dimensions of 40*700 mu m were realized with 0.5-dB insertion loss. >

Loss reduction for phased-array demultiplexers using a double etch technique

Wavelength Division Multiplexing (WDM) is an effective technique to exploit the huge bandwidth of optical fibres. Key components in such WDM-systems are demultiplexers which spatially separate the different wavelength channels. Phased-array demultiplexers combine ease of fabrication and low insertion losses. Silica-based phased-array demultiplexers are realised with low losses from 2-3 dB [1,2]. InP-based demultiplexers show slightly higher on-chip losses of 4-6 dB [3,4]. In addition they have considerably higher fibre coupling losses (several dB’s), but the advantage of InP-based demultiplexers is that they can be integrated with active components. Earlier we reported a low-loss demultiplexer with reduced fibre coupling loss by applying deeply etched InGaAsP waveguides with a relatively large core and a low index contrast, which had an almost circular mode profile [5]. The component had 4-5 dB on-chip loss and fibre coupling loss of about 1 dB to a tapered fibre. In this article we report a method to further reduce the on-chip losses.

A Tunable-MMI-Coupler-Based Wavelength Adjustable Laser

This paper introduces a novel integrated widely tunable laser, the tunable multimode interference (T-MMI) laser, with as tunable component an MMI coupler with a wavelength adjustable transmission spectrum. Experiments demonstrate up to 150 nm of tuning range for the T-MMI component and operation of a widely tunable T-MMI laser is demonstrated over a wavelength range of 38 nm.

System performance of a 4-channel PHASAR WDM receiver operating at 1.2 Gbit/s

Phased arrays are important key components in wavelength-division multiplexing (WDM) systems. We have realized a 4-channel WDM receiver combining a phased array with photodetectors on InP with a Si bipolar transimpedance amplifier. The channels are spaced at 2.0 nm with a 1.0-nm flat passband. On chip loss was 6-7 dB and detector efficiency was better than 90%. The optical cross talk remains below -20 dB. The electrical bandwidth per channel was 1 GHz. The electrical cross talk at 1 GHz after detection is below -25 dB. We have tested this receiver in a full 4-channel system.

Strained GaInAs/InP MQW layers grown by CBE for optical components

We investigated the influence of strain on the optical birefringence in waveguides consisting of Ga x In 1-x As/InP multiquantum well layers. The range of growth parameters to achieve good quality material for the waveguide structures were determined. In a number of layer structures low-loss optical waveguides and PHASAR demultiplexers were fabricated and characterized. The polarization dependence of the demultiplexer can be reduced by using quantum wells strained in tension. Without any precaution, the tensile strain in the well is limited by relaxation at e w ≃ - 0.8%. The strain in the well can be further increased to e w ≃ - 1% by introducing a strain-balancing layer of a compressive strained InAs monolayer in the InP barrier. But polarization independence is not yet achieved. The results indicate, that there is no negative effect of the strain-balancing layer on the optical performance. Also a number of design criteria for polarization independent waveguides are determined.

A COMPACT PHASED ARRAY BASED MULTI-WAVELENGTH LASER

Wavelength Division Multiplexing (WDM) is widely regarded as a promising option to increase the bandwidth and flexibility of broadband optical communication systems. In such systems, multi wavelength laser sources [I], both for selectable single wavelength and simultaneous multiple wavelength operation, will be important components.