Abstract: A wavelength meter for measuring the wavelength of an input light signal. The meter includes a beam splitter, a fixed mirror, and a moveable mirror, the beam splitter splits the input signal into a first input signal and a second input signal, the first and second input signals being reflected from the fixed and moveable mirrors, respectively, and being recombined by the beam splitter. The first reference light signal is reflected by the fixed mirror and the second reference light signal is reflected by the moving mirror, the beam splitter recombines the first and second reference light signals to form a combined reference light signal. The amplitude of the combined reference light signal is detected by a reference detector that generates a reference signal related to the amplitude of the combined reference light signal.

Abstract: An optical monochromator has high signal selectivity and low insertion loss, and is well-suited for characterizing a variety of optical signals, including closely-spaced optical channels within DWDM systems. The optical monochromator includes a bulk-optic polarization beam splitter that separates orthogonal polarization states of an applied optical signal into separate optical beams. Low insertion loss is achieved by reconciling the polarization states of the separate optical beams to an optimum polarization state that minimizes insertion loss when the optical beams are applied to a dispersive element. High signal selectivity is achieved using a multipass configuration and by illuminating large areas of the dispersive element, since large beam diameters are accommodated by the bulk-optic polarization beam splitter.

Abstract: An optical spectrum analyzer includes a polarization modifier that eliminates polarization-dependent wavelength spreading, enabling the analyzer to have high signal selectivity and high measurement sensitivity. The polarization modifier spatially separates orthogonal polarization components of the applied optical signal into separate optical beams and rotates the relative polarization components of the beams so that the beams are incident on a tunable interference filter in a multipass configuration at a single polarization state. The optical beams are directed through regions of the interference filter which lie on a contour of substantially equal center wavelength so that each of the multiple passes through the interference filter provides for corresponding narrowing of the filter bandwidth.

Abstract: An optical noise monitor measures noise power within narrow wavelength regions between channel signals of a dense wavelength division multiplexed (DWDM) signal. The noise monitor receives the DWDM signal and cascades the signal along a multipoint travel path where the signal is incident on a series of multi-pass filters. Each multi-pass filter selects a narrow, predefined wavelength region between channel signals of the DWDM signal. Noise power within the predefined wavelength region is detected and SNR is monitored by comparing the detected noise power to the power in the channel signal. According to a first preferred embodiment of the present invention, the noise monitor includes multi-pass filters that each have reflective surfaces to guide optical energy within a predefined wavelength region through multiple passes of an optical filter.

Abstract: A wavelength monitor detects wavelength drifts of component channel signals within multi-wavelength light signals. Multiwavelength light incident on the wavelength monitor is cascaded along a multipoint travel path. Within the travel path, the component channel signals are incident on a series of wavelength discriminators arranged on an optically transmissive member. Each wavelength discriminator is selectively transmissive to a predetermined one of the channel signals and is reflective to the remaining component channel signals of the multi-wavelength light signal. According to a first preferred embodiment of the present invention, the optical transmission through each wavelength discriminator varies monotonically according to variations in the wavelength of the predetermined channel signal. Each selectively transmitted channel signal is intercepted by a detector which produces an output current that is mapped to corresponding signal wavelengths.

Abstract: An optical cross-connect switch incorporates a pin grid actuator to selectively position optical elements relative to optical beams in the switch. A high density array of aligned, optically reflective elements is attached to the ends of independently selectable and moveable pins in the pin grid actuator. The pin grid actuator is the type extensively used in dot matrix printers. Linear motion of the pins causes the reflective element attached to the pin to intercept optical beams provided by input fibers coupled to the switch. Intercepted optical beams are redirected to designated output fibers, also coupled to the switch. A staggered arrangement of the input and output fibers equalizes all of the signal pathlengths through the switch, regardless of which pin in the pin grid actuator is selected. According to an alternate preferred embodiment of the present invention, multiple optical cross-connect switches are cascaded using a staggered arrangement of interconnecting fibers.

Abstract: The invention increases the tuning range of a laser by altering the output coupler reflectivity. In a first embodiment of the invention, the tuning range of an external cavity laser is increased by applying a substantially spectrally flat reflective coating to the front facet of a semiconductor laser which has higher reflectivity than the uncoated front facet. In addition to increasing the tuning range, the increased reflectivity of the front facet reduces the laser threshold current for all laser wavelengths. In a second embodiment of the invention, various complex coatings were applied to the output coupler to generate reflective characteristics that change according to wavelength. The complex coatings enhance reflectance at the edges of the laser tuning curve without adversely affecting the output power at the center wavelengths. This further increases the tuning range of the laser while simultaneously maintaining high output power for each selected output wavelength.

Abstract: A gradient-index (GRIN) rod lens for use in an optical receiver, in which the end face of the GRIN rod lens opposite a photodetector is bevelled. The resulting optical receiver achieves an optical return loss which is >10 dB higher than known optical receivers having a bevelled end solely on an optical launch side of the GRIN rod lens.

Abstract: Photodetectors having low reflectivity triangular groove, surface relief gratings on homogenous material or one layer of a heterostructure. Preferably, the photodetector is a PIN photodiode in which the p-type layer is triangularly grooved. The surface relief gratings have an optical repeat distance greater than the wavelenth of light which impinges on the photodetector surface. Thus, zero order backward diffracted waves are not coupled into optical reflections which would thereby decrease the optical return loss (ORL). Furthermore, the surface relief gratings have minimum side-wall angles to limit reflection at the heterostructure interfaces from contributing to the ORL. The side-angles of the gratings are chosen to ensure that the angle of the higher order backward diffracted wave is greater than the capture angle of an optical receiver into which the photodetector is incorporated. The free-space depth of the grooves is a half-wavelength of the light impinging on the photodetector.

Abstract: Photodetectors having low reflectivity triangular groove, surface relief gratings on homogenous material or one layer of a heterostructure. Preferably, the photodetector is a PIN photodiode in which the p-type layer is triangularly grooved. The surface relief gratings have an optical repeat distance greater than the wavelength of light which impinges on the photodetector surface. Thus, zero order backward diffracted waves are not coupled into optical reflections which would thereby decrease the optical return loss (ORL). Furthermore, the surface relief gratings have minimum side-wall angles to limit reflection at the heterostructure interfaces from contributing to the ORL. The side-angles of the gratings are chosen to ensure that the angle of the higher order backward diffracted wave is greater than the capture angle of an optical receiver into which the photodetector is incorporated. The free-space depth of the grooves is a half-wavelength of the light impinging on the photodetector.