An optical fiber fixing structure includes: a cylindrical member; an optical fiber inserted into a hole of the cylindrical member; and a fixing material configured to fix the cylindrical member and the optical fiber, wherein the optical fiber is a polarization maintaining optical fiber having a polarization axis, and a center of the optical fiber is arranged so as to be eccentric to a center of the hole, and an angle formed by an eccentric direction connecting the center of the hole and the center of the optical fiber and the polarization axis is 22.5 to 22.5, or 67.5 to 112.5.

An apparatus comprising a polarization beam splitter optically coupled to a first light path and a second light path and configured to receive a CW light having a plurality of wavelengths, forward a first light beam of the CW light along the first light path, and forward a second light beam of the CW light along the second light path. A first multiplexer coupled to the first light path and configured to de-multiplex the first light beam into a first plurality of channels each corresponding to one of the plurality of wavelengths. A second multiplexer coupled to the second light path and configured to de-multiplex the second light beam into a second plurality of channels each corresponding to one of the plurality of wavelengths. A modulator coupled to the first multiplexer and the second multiplexer and configured to modulate the first plurality of channels and the second plurality of channels.

An integrated polarization splitter and rotator (PSR) employs the TE0 and TE1 modes of propagating light, rather than the TE0 and TM0 modes used in conventional prior art PSR. The integrated PSR exhibits appreciably flatter wavelength response because it does not require a directional coupler to de-multiplex incoming polarizations. The PSR allows tuning of the TM0 loss to reduce polarization dependent loss (PDL). This integrated polarization splitter and rotator is applicable to all integrated platforms including Silicon-on-Insulator (SOI) and III-V semiconductor compound systems. The PSR may be very compact (122 m.sup.2), and provides low loss (<0.3 dB across the C-band) and ultra-broadband operation. The PSR also affords better control of polarization dependent losses.

Embodiments of the invention describe polarization insensitive optical devices utilizing polarization sensitive components. Light comprising at least one polarization state is received, and embodiments of the invention select a first optical path for light comprising a first polarization state or a second optical path for light comprising a second polarization state orthogonal to the first polarization state. The optical paths include components to at least amplify and/or modulate light comprising the first polarization state; the second optical path includes a polarization rotator to rotate light comprising the second polarization state to the first polarization state. Embodiments of the invention further describe optical devices including a polarization mode converter to convert light comprising a first and a second polarization state to light comprising different spatial modes of the first polarization state; light comprising the different spatial modes of the first polarization state is subsequently amplified and modulated.

Example polarization splitter and rotator devices are described. In one example, an optical apparatus includes a splitter configured to split a light signal into a first signal having a first polarization and a second signal having a second polarization, a polarization rotator configured to rotate the second polarization of the second signal into a third polarization, and a polarization mode converter configured to convert the third polarization of the second signal into the first polarization. In certain aspects of the embodiments, the splitter can be a curved multi-mode inference (MMI) polarization splitter, and the polarization rotator comprises input and output ports, with the output port being wider than the input port. The polarization mode converter can be an asymmetrical waveguide taper mode converter. The devices described herein can overcome the deficiencies of conventional devices and provide low insertion loss, flat and/or wide wavelength response, high fabrication tolerance, and compact size.

Embodiments of the invention describe polarization insensitive optical devices utilizing polarization sensitive components. Light comprising at least one polarization state is received, and embodiments of the invention select a first optical path for light comprising a first polarization state or a second optical path for light comprising a second polarization state orthogonal to the first polarization state. The optical paths include components to at least amplify and/or modulate light comprising the first polarization state; the second optical path includes a polarization rotator to rotate light comprising the second polarization state to the first polarization state. Embodiments of the invention further describe optical devices including a polarization mode converter to convert light comprising a first and a second polarization state to light comprising different spatial modes of the first polarization state; light comprising the different spatial modes of the first polarization state is subsequently amplified and modulated.

A wavelength selective switching device comprises a plurality of input paths for receiving optical signals, a plurality of output paths for emitting the optical signals, and a switching unit for selectively directing the optical signals from the input paths to the output paths. The switching unit comprises a reflective area adapted to be concurrently illuminated by a first optical signal from a first input path among the plurality of input paths, and by a second optical signal from a second input path among the plurality of input paths, the second input path being different from the first input path, and to concurrently direct the first optical signal to a first output path among the plurality of output paths and the second optical signal to a second output path among the plurality of output paths, the second output path being different from the first output path. Said first output path and said second output path are spatially separated by said first input path and said second input path, or vice-versa.

An integrated polarization splitter and rotator (PSR) employs the TE0 and TE1 modes of propagating light, rather than the TE0 and TM0 modes used in conventional prior art PSR. The integrated PSR exhibits appreciably flatter wavelength response because it does not require a directional coupler to de-multiplex incoming polarizations. The PSR allows tuning of the TM0 loss to reduce polarization dependent loss (PDL). This integrated polarization splitter and rotator is applicable to all integrated platforms including Silicon-on-Insulator (SOI) and III-V semiconductor compound systems. The PSR may be very compact (122 m.sup.2), and provides low loss (<0.3 dB across the C-band) and ultra-broadband operation. The PSR also affords better control of polarization dependent losses.

An optical module includes: an output section that outputs TM light; and a substrate-type optical waveguide. The substrate-type optical waveguide includes: a waveguide that guides the TM light outputted from the output section; a polarization rotating element that converts the TM light guided through the waveguide into TE light; and a function element that receives the TE light. In the optical module equation (aL)>(bL+c) is satisfies, where L is a length of the waveguide, a is a propagation loss of the TE light per unit length of the waveguide, b is a propagation loss of the TM light per unit length of the waveguide, and c is an insertion loss by the polarization rotating element.

Disclosed herein is an optical waveguide element that includes a substrate and a waveguide layer formed on the substrate and comprising lithium niobate. The waveguide layer has a slab part having a predetermined thickness and a ridge part protruding from the slab part. The maximum thickness of the slab part is 0.05 times or more and less than 0.4 times a wavelength of a light propagating in the ridge part.