Data centers and supercomputers are driving the demand for short reach aggregate bandwidth. E.g. active CXP active
optical cables (AOC) with an aggregate bandwidth of 120 Gbps  are being installed since about one year in some of
the biggest server farms in the world. As these applications require parallel optics, obviously this is a natural playground
for VCSEL technology. The 10G VCSEL platform of Philips ULM Photonics is enabling operation of such AOC at less
than 3 W total power by low bias currents for the individual VCSEL as low as 3.4 mA at room temperature and 5.5 mA
at 85°C ambient. In combination with ideally matched driver electronics, the launch power of the VCSELs can be
stabilized within 0.15dB variation across this operating temperature range  and thus allow for open loop power
control. With more than 108 hours of operation in the field and no field return reported, the FIT rate for the 1x12
VCSEL array can be calculated to be less than 10 FIT.
Over the past 3 years laser based tracking systems for optical PC mice have outnumbered the traditional VCSEL market
datacom by far. Whereas VCSEL for datacom in the 850 nm regime emit in multipe transverse modes, all laser based
tracking systems demand for single-mode operation which require advanced manufacturing technology. Next generation
tracking systems even require single-polarization characteristics in order to avoid unwanted movement of the pointer
due to polarization flips. High volume manufacturing and optimized production methods are crucial for achieving the
addressed technical and commercial targets of this consumer market. The resulting ideal laser source which emits
single-mode and single-polarization at low cost is also a promising platform for further applications like tuneable diode
laser absorption spectroscopy (TDLAS) or miniature atomic clocks when adapted to the according wavelengths.
Driving basic VCSEL technology in the '90, datacom has been the first volume market for various VCSEL products.
The downturn in 2001 can be regarded as a point in time, when engineers both from VCSEL manufacturers and nondatacom
users started to identify VCSEL technology as a very promising laser source platform for many other
applications. Dedicated spectroscopy laser sources based on VCSEL technology, e.g. for oxygen sensing , have
proven their competitiveness in industrial applications. The most prosepective consumer market of human-machineinterfaces
like laser mice has shown the huge potential of the VCSEL technology in low costs, high volume
applications, even given extreme technical performance specifications . Just as a consequence, VCSELs are now
penetrating into the next potential volume markets, where unique properties of this technology is requested: High power
pulsed laser applications, where low cost is a key factor for market entry. In this paper we discuss a suitable
semiconductor technology platform, assembly solutions, selected applications and their market potential as well as
performance and reliability data. From small footprint of 0.3 mm2 and 0.11 mm2 peak output powers of 0.7 W and more than 6 W at 850 nm wavelength are shown at 30 &mgr;s and 30 ns pulse widths, respectively.
Up to now applications for singlemode VCSELs were in low volume and high prized applications like tunable diode laser absorption spectroscopy (TDLAS, [1,2]) or optical interferometers. Typical volumes for these applications are in the range of thousands of pcs per year, with pricing levels of several 100 USD/pcs. New applications for singlemode VCSELs in consumer markets require manufacturing in very high volumes and at very low cost. Examples are laser-based optical mouse sensors, optical encoders, and rubidium atomic clocks for GPS systems [3,4]. U-L-M photonics presents manufacturing aspects, device performance and reliability data for these devices. The first part of the paper is dealing with high volume manufacturing of 850 nm singlemode VCSEL chips with very high efficiency and low operation current. Special processing technologies have been developed to achieve yields on 3 inch wafers of more than 90%. Wafer qualification procedures are discussed as well. The second part of the paper covers high volume packaging in TO and SMT type packages where very high packaging yields must be achieved. In the last part of the paper reliability issues are discussed, focused on the very high susceptibility of these devices to electrostatic discharge.
The growing demand on low cost high spectral purity laser sources at specific wavelengths for applications like tuneable diode laser absorption spectroscopy (TDLAS) and optical pumping of atomic clocks can be met by sophisticated single-mode VCSELs in the 760 to 980 nm wavelength range. Equipped with micro thermo electrical cooler (TEC) and thermistor inside a small standard TO46 package, the resulting wavelength tuning range is larger than +/- 2.5 nm. U-L-M photonics presents manufacturing aspects, device performance and reliability data on tuneable single-mode VCSELs at 760, 780, 794, 852, and 948 nm lately introduced to the market. According applications are O2 sensing, Rb pumping, Cs pumping, and moisture sensing, respectively. The first part of the paper dealing with manufacturing aspects focuses on control of resonance wavelength during epitaxial growth and process control during selective oxidation for current confinement. Acceptable resonance wavelength tolerance is as small as +/- 1nm and typical aperture size of oxide confined single-mode VCSELs is 3 μm with only few hundred nm tolerance. Both of these major production steps significantly contribute to yield on wafer values. Key performance data for the presented single-mode VCSELs are: >0.5 mW of optical output power, >30 dB side mode suppression ratio, and extrapolated 10E7 h MTTF at room temperature based on several millions of real test hours. Finally, appropriate fiber coupling solutions will be presented and discussed.
Following the success in fiber based DataCom, VCSELs start to conquer additional market shares in a variety of other
applications like free space optics (FSO), lighting, printing, and sensing. U-L-M photonics presents a new family of
commercial high power VCSELs emitting powers of up to 50 mW cw at RT based on top-emitting technology. The
devices are available at 850 nm emission wavelength. All devices can be operated passively cooled and provide
modulation bandwidths of up to 1 GHz. Wallplug efficiencies are in excess of 25 %. Even higher output power of 250
mW cw from a 80 μm active diameter bottom-emitting VCSEL operating at 980 nm has already been obtained although
just beeing passively cooled. Further power up scaling is achieved by arrangement of multiple VCSELs in 2D arrays.
For the first time we demonstrate cw output power of 10 Watt cw at RT from compact monolithic VCSEL module of 14
mm2 chip area. Transfer of the technology to other wavelengths, e.g. 808 nm and 945 nm, is presented, too, and shows
perspectives towards homogeneous optical pumping of solid state lasers. Almost identical device performance levels
can be presented for the entire wavelength span. All discussed results are based on highest quality epitaxy optimized for
maximum intrinsic efficiency and differential slope efficiency. Oxide confinement is used for current constriction that
provides most efficient electrical pumping of the active area. In combination with advanced mounting techniques all
mentioned aspects sum up to allow for cost effective VCSEL products in the medium and high power laser regime. The
circular output beam in addition to simple heat sinking offers attractive solutions for advanced system integration.
We report on recent progress in the design and application of
vertical-cavity surface-emitting lasers (VCSELs) for optical
interconnect applications in the 850 nm emission wavelength
regime. Ongoing work toward parallel optical interconnect modules
with channel data rates of 10 Gbit/s is reviewed and performance
results of flip-chip integrated two-dimensional VCSEL arrays are
presented. 10 Gbit/s speed as well as low thermal resistance of
the lasers has been achieved. As a possible alternative to
graded-index multimode fibers, we show 10 Gbit/s data
transmission over 100 m length of a novel, entirely undoped
multimode photonic crystal fiber. The use of VCSELs with output powers in the 10 mW range is demonstrated in a 16-channel free-space optical (FSO) module and VCSELs with even higher output power are shown to provide possible FSO connectivity up to data rates of 2.5 Gbit/s.
There is a wide variety of reasons why future high-performance datacom links are believed to rely on two-dimensional VCSEL arrays suitable for direct flip-chip hybridization. Some typical are as follows: highest interconnect density, high-frequency operation, self alignment for precise mounting, productivity at high number of channels per chip. In this paper the latest approaches to flip-chip VCSELs are presented. In particular we will asses the properties of transparent substrate VCSEL arrays which are soldered light-emitting side up as well as VCSEL arrays which are soldered light-emitting side down, e.g., onto a CMOS driver chip. The VCSEL arrays are designed for bottom- or top-emission at 850 nm emission wavelength and modulation speeds up to 10 Gbps per channel.
U-L-M photonics GmbH has been set up to develop next-generation vertical-cavity surface-emitting laser (VCSEL) products and to exploit the full potential of these industry-leading devices in terms of performance and application areas. Reliability is important for all application areas for VCSELs. This paper presents the excellent reliability characteristics of U-L-M’s VCSEL technology. Accumulation of all advantageous properties VCSELs are famous for, like low power consumption, circular low divergent beam profile, high modulation bandwidth, and scalability of monolithic arrangements, results in two-dimensional (2D) VCSEL arrays that appear as key components to reach highest aggregate bandwidths of tomorrow’s parallel optical transceivers. We report on 2D VCSEL arrays, substrate emitting although operating at 850 nm and prepared for flip-chip bonding, that are well suited for the customer’s needs in terms of speed, power consumption, and compact integration. Up to now, in most single channel transceivers, the VCSEL is packaged in a TO can and connected to the driver via a printed circuit board. We investigate the performance of a high speed VCSEL in a TO 46 package and demonstrate 10 Gbps transmission. The potential of VCSEL technology in other areas of application than datacom or telecom is just going to be exploited. We present a 760 nm single-mode VCSELs for gas monitoring applications.
We report on recent progress in the design of short-wavelength vertical-cavity surface-emitting lasers (VCSELs) for 10 Gbit/s datacom applications. Topics of interest include differential mode delay characterizations of high-performance multimode fibers and their interplay with transverse single- and multimode VCSELs, flip-chip integrated two-dimensional arrays at 850 nm wavelength, as well
as experiments toward the realization of optical backplanes. In
the latter case, reliable 10 Gbit/s data transmission has been
achieved over low-loss integrated polymer waveguides with up to 1
meter length. Moreover we present VCSELs with output powers in the 10 mW range that are employed in multi-beam transmitters for free-space optical data transmission with Gbit/s speed over distances of up to about 2 km.
Accumulation of all advantageous properties VCSELs are famous for, like low power consumption, circular low divergent beam profile, high modulation bandwidth, and scalability of monolithic arrangements, results in two-dimensional (2D) VCSEL arrays that appear as key components to reach highest aggregate bandwidths of tomorrow's parallel optical transceivers. We report on 2D VCSEL arrays, substrate emitting although operating at 850 nm and prepared for flip-chip bonding, that are well suited for the customer's needs in terms of speed, power consumption, reliability and compact integration. Based on advanced technology, our arrays target the requirements of transceivers in the OC-192 VSR and 10 Gigabit Ethernet arena. In this paper we present the basic technology, static and dynamic device characteristics as well as reliability data for a 4x12 850 nm bottom-emitting VCSEL array. A13
Oxide-confined vertical-cavity surface-emitting laser diodes (VCSELs) are optimized for multi-Gbit/s data rate optical transmission systems. Noise characteristics and small-signal modulation response of high-performance transverse single- and multi-mode devices under different operation conditions are investigated. We demonstrate for the first time 12.5 Gbit/s data rate fiber transmission with a bit-error rate of better than 10-11 for pseudo-random bit sequence signals over 100m multimode fiber and 1 km single-mode fiber. Maximum electrical and optical bandwidths obtained at 3 mA driving current are 12 GHz and 13 GHz, respectively. For pumping levels above 2.8 times threshold current, the relative intensity noise is below -150 dB/Hz up to 5 GHz for output powers of about 1mW. In detail, we investigate the low frequency intensity noise of high efficiency small area selectively oxidized VCSELs emitting in the fundamental transverse mode up to 7 times threshold current at room temperature and in multiple transverse modes up to 20 times threshold current. For low temperature operation quantum efficiency of the VCSEL is increased leading to photon- number fluctuations 1.4 dB below the shot noise limit. This is to our best knowledge the largest amount of squeezing ever reported for VCSELs.
We have designed and fabricated a 64 channel optical module using a self-alignment flip-chip packaging technique for 2D GaAs epitaxial-side emitting vertical-cavity surface- emitting laser (VCSEL) array mounting without substrate removal on Si subcarrier. Light emission is obtained through a wet-chemically etched window in the Si subcarrier. The 2D independently addressable selectively oxidized GaAs laser array is arranged in an 8 X 8 matrix with a device pitch of 250 micrometers and each laser is supplied with two individual top contacts. This metallization scheme allows flip-chip mounting junction-side down on Si subcarrier. The VCSEL array chip is placed above the window in the Si subcarrier and is assembled using a self-aligned bonding technique with PbSn solder bumps. Arrays with 4 micrometers active diameter investigated before and after packaging show quite homogeneous optical and electrical continuous wave output characteristics exhibiting threshold currents of less than 1.1 mA and single-mode output powers of 2 mW. Driving characteristics of the lasers in the array are fully compatible to advanced 3.3 V CMOS technology. The modules are used to demonstrate free-space directional transmission applying beam steering.
Oxide-confined vertical cavity surface-emitting laser diodes (VCSELs) are fabricated for applications in chip-level optical interconnects. 980 nm wavelength devices in arrays with 4 by 8 elements are investigated. Threshold voltages of 1.5 V and operation voltages below 2V of submilliamp threshold current lasers are fully comparable to 3.3 V CMOS technology. Modulation bandwidths of 9.5 GHz at 1.8 mA laser current with a modulation current efficiency factor of 10 GHz/(root)mA is demonstrated for 3 micrometers diameter VCSELs. No error floors are observed down to bit error rates of 10-11 at 12.5 Gb/s data transmission. VCSEL based top illuminated resonant cavity enhanced photodetectors show peak efficiencies of 50 percent combined with full spectral half-widths of 5 nm.
We present a novel smart pixel composed of an optoelectronic threshold switch with gain and a vertical cavity surface-emitting laser (VCSEL). In this smart pixel two surface-normal input optical beams control an output optical beam emitted by the VCSEL. In its present hybrid version the VCSEL-based smart pixel is capable of opto-optical switching with an output contrast ratio in excess of 30 dB at an optical power of about 1.5 mW. For quasi-stationary operation we achieve an optical gain of up to 3 X 105. We also report drastic improvements on the switching dynamics. Operating the receiver with an optical input power of 130 (mu) W we achieve bitrates of up to 160 Mbit/s and an optical gain of 11, while optical inputs of 410 (mu) W result in a maximum bitrate of 400 Mbit/s and an optical gain of 3.6. The minimum input optical energy required for switching is 765 fJ, the AC output contrast ratio is 9 dB. Optically performed NAND and NOR logic operations are demonstrated at 40 Mbit/s with a fan-out of 7.6. We further show that the functionality of this smart pixel can easily be extended to electric read-out of input optical data and to direct electric control of the VCSEL within the smart pixel configuration. In particular, we demonstrate conversion of electric input to optical output data at 1 Gbit/s.