Multiple-wavelength Vertical-cavity Surface-emitting Laser Arrays Research Articles

Growth of highly strained GaInAs-GaAs quantum wells on patterned substrate and its application for multiple-wavelength vertical-cavity surface-emitting laser array

We carried out the growth of highly strained GaInAs-GaAs quantum wells (QWs) on a patterned substrate for extending emission wavelength on a GaAs substrate. We examined the shift of photoluminescence wavelength of the QWs and showed a large wavelength shift due to the spatial modulation in well thickness and indium composition. We demonstrated a single-mode multiple-wavelength vertical-cavity surface-emitting laser (VCSEL) array on a patterned GaAs substrate covering a new wavelength window of 1.1-1.2 /spl mu/m. By optimizing pattern shape, we achieved multiple-wavelength operation with widely and precisely controlled lasing wavelengths. The maximum lasing span is as large as 77 nm. We carried out a data transmission experiment through 5-km of single-mode fiber with a 2.5 Gb/s/channel. The total throughput reaches 10 Gb/s. The VCSEL-based wavelength-division-multiplexing (WDM) source would be a good candidate for WDM-LAN beyond 10 Gb/s.

RF crosstalk in multiple-wavelength vertical-cavity surface-emitting laser arrays

We present the crosstalk measured in multiple-wavelength vertical-cavity surface-emitting laser (VCSEL) arrays under RF modulation. The array consists of eight bottom-emitting VCSEL's arranged with a "pie"-like configuration within a 60-μm-diameter circle with a 3-μm spacing for coupling into a multimode fiber. The crosstalk is investigated by measuring a cross-modulation response of two VCSEL's in the array using a monochromator in an optical spectrum analyzer as a receiver. Excess crosstalk is minimized by flip-chip mounting the array and introducing a proper bias condition. The crosstalk observed In the adjacent VCSEL's is less than -40 dB at the modulation frequency below 700 MHz and it Increases at 20 dB/decade above this frequency when both VCSEL's are biased at 5.0 mA.

Monolithic oxide-confined multiple-wavelength vertical-cavity surface-emitting laser arrays with a 57-nm wavelength grading range using an oxidized upper Bragg mirror

Monolithic, oxide-confined, multiple-wavelength vertical-cavity surface-emitting laser arrays with a very large periodic, wavelength grading span of 57 nm (from 968 to 1025 nm) have been achieved under room temperature, continuous-wave operation, with threshold currents of 4.5 mA/spl plusmn/1.5 mA. Almost linear wavelength grading is achieved by organometallic vapor phase epitaxial growth on a patterned substrate. An extended wavelength range is achieved by minimizing the optical loss dispersion by scaling the growth rate of all the epilayers and using a selectively-oxidized upper DBR mirror with a flattened optical reflectance spectrum, plus the higher differential optical gain provided by compressively-strained In/sub 0.2/Ga/sub 0.8/As-GaAs quantum wells.

Oxide-confined monolithic, multiple-wavelength vertical-cavity surface-emitting laser arrays with a 40-nm wavelength span

Monolithic, multiple-wavelength, vertical-cavity surface-emitting laser arrays grown by controlling the metal-organic chemical vapor deposition epitaxial growth rate on a patterned substrate, and using selective oxidation for current confinement, have been demonstrated with a periodic, graded wavelength span of 40 nm, Near room-temperature, electrically pumped continuous-wave lasing is achieved over the entire 40-nm range, with uniform threshold currents of 4.5 mA/spl plusmn/1.0 mA, and with output powers ranging from 0.4-1.3 mW.

Monolithic, multiple-wavelength vertical-cavity surface-emitting laser arrays by surface-controlled MOCVD growth rate enhancement and reduction

Monolithic, multiple-wavelength vertical-cavity surface-emitting laser (VCSEL) arrays have been obtained by the surface-controlled enhancement and reduction of the MOCVD epitaxial growth rate, achieving a periodic, graded wavelength span greater than 30 nm. Room-temperature (RT), electrically pumped continuous-wave (CW) lasing is demonstrated, with uniform threshold currents of 5.5/spl plusmn/0.5 mA with typical output powers of 0.5 mW. We show here for the first time both the enhancement and the reduction of the growth rate of the entire VCSEL structure and demonstrate the controlled variation of the VCSEL lasing wavelength over a widened spectral range by exploiting both effects.

Reduced switching delay in wavelength division multiplexed two-dimensional multiple-plane optical interconnections using multiple-wavelength VCSEL arrays

We calculate the expected number of internodal hops for a network established with a wavelength division multiplexed (WDM) two-dimensional (2-D) multiple-plane optical interconnection. This WDM optical interconnection incorporates WDM pixels consisting of multiple-wavelength vertical-cavity surface-emitting laser (VCSEL) arrays and wavelength-selective detectors. The WDM interconnection can support simultaneous and reconfigurable communication among a network of nodes, Using the expected number of hops as a measure of internodal switching delay, we show that the integration of WDM into the interconnection results in a significantly reduced delay as compared to single-wavelength systems. Substantial delay reduction results even when the number of wavelengths is small relative to the number of 2-D planes. We analyze the bus, dual-bus, and ring architectures since they define the means of communication between pixels. For each architecture, we analyze three configurations which provide each node access to (i) an entire plane of pixels, (ii) a row (or column) of pixels, or (iii) an individual pixel. When each network node has access to an entire plane of pixels, the proposed WDM interconnection incurs substantially shorter delay than single-wavelength optical interconnections. By allowing a node to access an entire row or column of pixels, the interconnection benefits from the incorporation of spatial division multiplexing (SDM) and the number of nodes connected can grow substantially, with negligible added delay. Finally, when a node can access only a single pixel, a large number of independent processors can be interconnected exhibiting far less switching delay than other electronic or optical interconnections of comparable size.

Multiple-wavelength vertical-cavity surface-emitting laser arrays with a record wavelength span

Multiple-wavelength vertical-cavity surface-emitting laser (VCSEL) arrays are fabricated using a modified patterned-substrate growth technique in a molecular beam epitaxy (MBE) system. We achieved a large lasing wavelength span of 62.7 nm and highly uniform threshold currents with an average of 2.16/spl plusmn/0.81 mA. High repeatibility of wavelength spacing between 15 arrays with sharp wavelength shift rate 117.14 nm/mm is achieved.

VERTICAL CAVITY SURFACE EMITTING LASER ARRAYS FOR WAVELENGTH DIVISION MULTIPLEXING APPLICATIONS

The capability to fabricate two-dimensional (2D) semiconductor diode laser array is one of the most important steps towards making wafer-scale low-cost lasers. The recent emergence of vertical cavity surface emitting laser (VCSEL) facilitates the fabrication of such large 2D arrays. In this paper, we review the recent progress on a novel largeaperture single-mode VCSEL and a 2D multiple-wavelength VCSEL array for ultra-high bandwidth applications. We demonstrate a passive antiguide region (PAR) VCSEL which emits a stable single mode with very low threshold, a large aperture, and a fixed polarization. We also demonstrate multi-wavelength VCSEL arrays with repeatable wavelength spans over 20 nm, grown by Molecular Beam Epitaxy. The wavelength shift is achieved by varying the GaAs growth rate across the wafer using a patterned backing wafer to induce a temperature profile. Such multiple wavelength laser arrays are promising for ultrahigh bandwidth optical transmission and switching systems using wavelength division multiplexing (WDM).