Optical bench assembly and fabrication method

Details Optical bench assembly and fabrication method Optical bench assembly and fabrication method

2000-12-14

2002-10-22

Epps, Georgia (Department: 2873)

Optical: systems and elements

Lens

With support

C385S033000

Reexamination Certificate

active

06469843

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to receivers for optical telecommunications applications, and more particularly to silicon optical benches used therein.
BACKGROUND OF THE INVENTION
Silicon optical benches typically comprise a single crystal semiconductor such as silicon as a base material upon or within which an optoelectronic device subassembly is constructed. Silicon optical benches may be used to fabricate receiver modules for optical telecommunications. As depicted in
FIG. 1
a receiver module may include a photodetector
102
and a mirror
104
to direct incident radiation from an optical fiber
106
onto the photodetector active region
108
. Typically, the incident light is focused onto mirror
104
by a coupling lens
110
. The bench facilitates the alignment of light from fiber
106
such that it focuses on mirror
104
. Mirrors may be formed directly in the silicon bench by etching along the (1,1,1) plane and coating the resulting exposed face or faces with aluminum or gold. The etched planes for silicon are at an angle of 35.7° to the incident light, which results in a reflection which is 108.6° from the optical axis. The optimum reflection angle, however, for directing incident light onto photodetector active region
108
is typically 90°. Accordingly, light incident on photodetector
102
is at an 18.4° angle relative to the surface normal, and therefore, may miss active region
108
.
As shown in
FIG. 2
, when a lensed photodetector
202
is used, a focus spot
204
is formed away from the center of the active photodetector region
206
. In this configuration 60% to 75% of the focused light may miss active region
206
. This may lead to decreased coupling efficiency and lower overall signal levels on the receiver.
A lens may be formed on the photodetector surface to concentrate the light into a smaller area, and thereby increase the coupling efficiency. The disadvantage of this approach is that some or all of the light is likely to be incident outside of the active area of the photodetector when a mirror etched on the silicon bench is used.
Increasing the active region of the photodetector may compensate for alignment problems caused by mirrors etched in the silicon (1,1,1) plane. This, however, has the undesirable effect of increasing device capacitance, and therefore, reducing the usable bandwidth of the device due to the increase response time constant. This may also lead to a need for larger devices to generate the same photocurrent. As device size increases, fewer devices may be fabricated from a single wafer, thereby increasing the cost per device.
Accordingly, there is a need to accurately focus incident radiation on the active region of a photodetector in an optical subassembly bench when a mirror position in the subassembly is dictated by the crystal structure of the bench material.
SUMMARY OF THE INVENTION
An optical lens for use with an optical bench is disclosed. The lens consists of a diffractive element which provides an angular offset to radiation incident on the lens while allowing it to be focused to a point. The angular offset substantially compensates for an undesirable focal point location caused by a variance between an integral component position on the bench and a desired position. The lens is particularly useful wherein an integral component position is dictated by the bench crystal structure. In an illustrative embodiment the diffractive element is aspheric and deflects incident radiation by an amount in the range of about 8° to about 12° to compensate for the focal point location produced by an integral component positioned on a silicon (1,1,1) plane.
Further disclosed is a method of compensation for variance between an integral component position on a bench and a desired position. Still further disclosed are an optical bench. a method for fabricating an optical bench and a semiconductor device.


REFERENCES:
patent: 4983009 (1991-01-01), Musk
patent: 5066089 (1991-11-01), Greil et al.
patent: 5229883 (1993-07-01), Jackson et al.
patent: 5684901 (1997-11-01), Gaebe
patent: 6091756 (2000-07-01), Bylsma
patent: 6157502 (2000-12-01), Kathman
patent: 6215925 (2001-04-01), Kaneyama
patent: 6252725 (2001-06-01), Tran et al.
Meyers, Mark M., entitled “Diffractive optics at Eastman Kodak”, SPIE vol. 2689, pp. 228-254, Aug. 1996.

Affiliated with

Also associated with

Rating

Optical bench assembly and fabrication method does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Optical bench assembly and fabrication method, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Optical bench assembly and fabrication method will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2999640