Reducing polarization dependency of optical apparatus

Details Reducing polarization dependency of optical apparatus Reducing polarization dependency of optical apparatus

2000-03-06

2001-10-16

Spyrod, Cassandra (Department: 2872)

Optical: systems and elements

Polarization without modulation

Polarization using a time invariant electric, magnetic, or...

C359S490020, C359S490020, C359S900000, C385S011000

Reexamination Certificate

active

06304380

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to optical apparatus such as equalizers having chromatically variable transmissivity and, more particularly, to reducing the polarization dependency of such apparatus.
BACKGROUND OF THE PRIOR ART
A class of devices employing waveguide gratings interconnected by a waveguide lens and functioning as a dynamic optical wavelength power equalizer is described in C. R. Doerr, et al, “Dynamic wavelength equalizer in silica using the single-filtered-arm interferometer”, IEEE Photon. Technol. Lett., vol. 11, pp. 581-583, 1999. Other examples include wavelength-selective cross connects and large-channel-count wavelength add-drop filters. The aforementioned article points out that a ripple-free spectrum can be achieved for a cascaded grating-lens-grating device by taking care not to under-sample the spectrum at the lens inlets to the star couplers. In previous designs, both the grating and lens inlet center-to-center spacings in the inner star couplers were dimensioned to minimize loss and achieve small size. Unfortunately, small size tends to produce significant mutual coupling among both the grating and lens inlets which results in a periodic phase distortion of the light when it reaches the grating arms. Likewise, the mutual coupling in the grating inlets results in a periodic phase distortion of the light when it reaches the lens arms, the periods being equal to the Brillouin zone widths. In addition to these effects, polarization-dependent loss (PDL) limits the usefulness of the equalizer, and for many applications the PDL must be <0.1 dB over the entire spectrum of interest and, even when good engineering practices are followed it is not unusual to have a PDL of more than 5 dB. Reducing polarization dependency in optical devices such as equalizers having chromatically variable transmissivity would yield a device that is more generally useful in wavelength-division multiplexed networks.
SUMMARY OF THE INVENTION
In accordance with the principles of our invention, in one aspect thereof, polarization dependency in optical apparatus, such as equalizers having chromatically variable transmissivity, is reduced by splitting the light incoming to the apparauts into orthogonally polarized streams and directing the streams to pass through the apparatus in opposite directions. In an illustrative embodiment, an equalizer comprising a planar glass Mach-Zehnder interferometer is fabricated on a chip having a waveguide in one of its arms and a cascaded grating-lens-grating in the other. Phase distortion is advantageously compensated by adjusting the arm lengths in the grating and lens as disclosed in the above-referenced related copending application to reduce loss and optical crosstalk among the spectral control points. Polarization dependencies exhibited by components of the interferometer are eliminated by splitting the incoming stream to be equalized into two orthogonally polarized streams which are applied to opposite ends of the equalizer chip through polarization maintaining fibers oriented such that the light polarization is the same on the chip for both directions and is aligned with one of the chip's eigenpolarizations. The light streams pass through the waveguide and through the cascaded grating-lens-grating in opposite directions and are recombined and applied to the opposite polarization maintaining fiber from which they entered the equalizer. The split streams are then spectrally re-combined and directed to the output. Advantageously, the incoming light stream entering one port of a circulator and emerging from a second port is applied to the splitter on its way to the equalizer while the light streams from the equalizer after being spectrally recombined re-enter the second port of the circulator and emerge from its third port to the output thereby eliminating any polarization dependencies of the interferometer.


REFERENCES:
patent: 5388001 (1995-02-01), Okayama et al.
patent: 5481402 (1996-01-01), Cheng et al.
patent: 5638473 (1997-06-01), Byron
patent: 5708734 (1998-01-01), Van Der Tol
patent: 5809184 (1998-09-01), Doerr et al.
patent: 5864421 (1999-01-01), Suzuki et al.
patent: 5946129 (1999-08-01), Xu et al.
patent: 0 482 461A1 (1992-04-01), None
patent: 8-5977 A (1996-01-01), None
patent: 8-184789 A (1996-07-01), None
patent: 9-146020 A (1997-06-01), None
patent: 11-271817 A (1999-10-01), None
M. Fukutoku, et al., “Wavelength-Division-Multiplexing Add/Drop Multiplexer Employing a Novel Polarisation Independent Acousto-Optic Tunable Filter”, Electronics Letters, vol. 29, No. 10, pp. 905-907, May 1993.*
Norio Takato, et al., “Silica-Based Integrated Optic Mach-Zehnder Multi/Demultiplexer Family with Channel Spacing of 0.01-250 nm.” IEEE J. Selected Areas in Comm., vol. 8, No. 6, pp. 1120-1127, Aug. 1990.*
Norio Takato, et al., “Silica-Based Single-Mode Waveguides on Silicon and their Application to Guided-Wave Optical Interferometers”, J. Lightwave Technology, vol. 6, No. 6, pp. 1003-1010, Jun. 1988.

Affiliated with

Also associated with

Rating

Reducing polarization dependency of optical apparatus does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Reducing polarization dependency of optical apparatus, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Reducing polarization dependency of optical apparatus will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2552912