David M. Braun

Broadband multilayer antireflection coating for semiconductor laser facets

Using a triple-layer antireflection coating of Al(2)O(3), Si, and SiO(2), we have achieved a minimum facet reflectivity of 1 x 10(-6) and a bandwidth of 90 nm for a reflectivity of 5 x 10(-5) or less for 1550-nm center-wavelength InGaAsP semiconductor lasers. A facet reflectivity of 3 x 10(-6) and a bandwidth of 30 nm for a reflectivity of 5 x 10(-5) were achieved for 1310-nm InGaAsP lasers. This coating is applicable to broadband external-cavity-tuned laser sources, edge-emitting light-emitting diodes, and semiconductor laser amplifiers.

Design of single layer antireflection coatings for InP/In 0.53 Ga 0.47 As/InP photodetectors for the 1200–1600-nm wavelength range

Single layer antireflection coatings have been designed and fabricated for frontside illuminated InP/ In(0.53)Ga(0.47)As/InP photodetectors with normal incident light over the 1200-1600-nm wavelength range. The design treats the InP and InGaAs layers as the bottom two layers of a triple layer antireflection coating. A euating fabricated using plasma enhanced chemical vapor deposited silicon nitride demonstrated <0.5% reflected power at both 1312- and 1559-nm wavelengths simultaneously. The design method used, four antireflection coating designs, and measurement results from fabricated samples using two of the designs are presented.

High-power semiconductor edge-emitting light-emitting diodes for optical low coherence reflectometry

A new semiconductor source was designed for optical low coherence reflectometry, increasing the sidelobe-free dynamic range by three to five orders of magnitude compared to conventional EELEDs. Reflectivities internal to an optical fiber circuit separated by as much as eight orders of magnitude can now be detected at wavelengths of 1.3 and 1.55 /spl mu/m, using compact semiconductor sources. For applications not requiring sidelobe-free operation, the same devices can be operated at high current (200 mA) and low temperatures (near 0/spl deg/C) to produce nearly 1 mW of 1.5 /spl mu/m emission coupled into single-mode fiber. The resulting wavelength spectrum is smooth, enabling fiber-based absorption spectral measurements. >

Optical Reflection Measurement System Using A Swept Modulation Frequency Technique

A measurement system has been developed capable of mea-suring reflected optical power as low as 0.0025% with a spot size diam-eter of 24 Am. One application for this system is the characterization of small-area photodetectors. The operation of the measurement system is simple, allowing the operator to quickly make multiple reflection measurements, and it does not require a darkroom. The measurement system merges a microscope, for visual alignment and focusing of the laser beam, with a lightwave component analyzer using modulation vec-tor error correction. A measurement comparison between the analyzer-based system and a power-meter-based system showed that each sys-tem can measure reflections as low as 0.0025%. However, the analyzer-based system offers the advantage of identifying the location and magnitude of system reflections. The system operates at a wavelength of 1310 nm.

Wavelength-dependent optimum output coupling enhances performance of external-cavity-tuned semiconductor lasers at 1.5 /spl mu/m

The output power of an external-cavity-tuned laser has been significantly increased by using an output coupler with a wavelength-dependent reflectivity. Our algorithm for determining the optimum wavelength dependence uses a simple gain model, and all necessary parameters can be determined from measurements of the same actual gain medium that will be used in the tunable laser source. This approach also increases tuning range.

Improved throughput of deep high-aspect-ratio trenches using split-beam laser ablation

A 20W 355nm DPSS Q-switched nanosecond pulse width laser, with external beam-splitting optics, was used to simultaneously ablate two 600μm deep, 140μm wide, 13.4mm long blind trenches in silicon using a five line wide cut strategy, achieving a 1.22x throughput improvement compared with a single-beam 20W laser configuration. Improved split-beam throughput was achieved because overhead time consisting of non-cut time during galvanometer retrace and turn-around movements and the time taken to ablate shoulder formations, were found to be approximately independent of laser power. With this split-beam approach, where two identical trenches are simultaneously cut, overhead time is split between the two trenches when cut time/die is calculated, halving the effective overhead time/die, and thereby improving throughput. Specific throughput improvement depends upon cut strategy, trench size, and insertion loss of the beam-splitting optics. Beam splitting optics consisted of a half-wave plate, Glan-laser polarizing prism, and mirror. Making use of the linear polarization characteristic of laser light, rotation of the half-wave plate was used to adjust the relative power in each beam, and thereby equalize the ablation rate of each beam. Adjustment of the mirror angle determined the separation between the two trenches.

Optical receiver design for high optical return loss

A new fiber pigtailed optical receiver design using a single gradient-index rod lens with a beveled exit face achieved a broadband optical return loss of > 65 dB, which was limited by the diffuse reflection from the photodetector front surface. By contrast the optical return loss for a receiver with an unbeveled lens exit face and an on-axis optical path was limited to a smaller value by the specular reflection from the lens exit face.

Low reflectivity triangular groove surface relief gratings for lnP/ln 0.53 Ga 0.47 As/lnP photodetectors

Less than 0.035% reflected optical power from an InP/InGaAs/InP photodetector structure was achieved at wavelengths of 1300 nm and 1550 nm for a 24-microm diameter spot size of unpolarized light. A triangular groove surface relief grating and an antireflection overcoating were used to achieve this performance level. The grating was fabricated in the InP top layer by a novel process based on an ion mill technique. This approach may be used to improve the optical return loss of high speed optical receivers. The reflected power measurements were made using a system of N.A. = 0.05 with an objective lens whose optical axis was normal to the grating.