US 4,758,090 AGranted

Optical wavelength monitor using blazed diffraction grating

AssigneeAllied-Signal Inc.

InventorRichard F. Schuma

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Abstract

A wavelength monitor (25) uses a diffraction grating (35) and a beam splitter (31). Light from a superluminescent diode (SLD) is supplied to the beam splitter (31) and is projected onto the grating (35). The grating is formed by holographically projecting a diffraction pattern onto a polished surface which is then photoetched, thereby creating a blazed diffraction grating corresponding to the projected pattern. The etched grating is used as a master, wherein the etched grating is coated with reflective material. The reflective material is then transferred to a prepared substrate that has an ultra-low thermal expansion coefficient to form a low cost replica diffraction grating. The grating (35) formed in this manner becomes a very stable and efficient dispersive element that forms a spectrum of the SLD output that is free of ghost images and accurately deproduces the spectral distribution. A pair of optical sensors (41, 42) detect an imbalance in reflected light, providing an indication of wavelength deviation.

Claims13

Dependent claims

Fiber optic gyroscope including, a broadband light source, a fiber optic coil, means to detect a Sagnac phase shift as a result of light passing through the fiber optic coil and a wavelength monitor to provide a wavelength deviation signal for controlling the light source, comprising:

(a) a blazed reflective diffraction grating;
(b) means to transmit light from the fiber optic coil to the blazed reflective diffraction grating, said means including light collimating means capable of protecting the light onto a significant surface area of the blazed refraction grating;
(c) a beam splitter receiving said light reflected from the refraction grating;
(d) the light supplied to a wavelength monitor being transmitted through the beam splitter to the collimating means;
(e) the light reflected into the beam splitter being transmitted through the collimating means in a manner which focuses the reflected light into the beam splitter;
(f) optical sensor means to detect an unbalanced state of the light entering the beam spliter;
and
(g) the light reflected from the blazed diffraction grating being retroflected through the collimating means back to the beam splitter so that the optical sensor means detects an offaxis condition of the reflected light.

5 more elements

Interferometer including a coherent light source generating coherent light, a wavelength monitor, and means to conduct the coherent light to the wavelength monitor, characterized by the wavelength monitor including:

(a) a blazed reflective diffraction grating formed by preparing a master surface having a blazed diffraction grating pattern thereon, depositing of a parting material on the master, coating of the master with a reflective material, the reflective material being coated over the parting material, preparing a surface of a new substrate so as to permit the reflective material to be bonded to the new substrate, bringing the surface of the new substrate into contact with the coated surface of the master, and separating the surfaces in a manner which results in the reflective coating material remaining bonded to the new substrate and becoming separated from the master;
(b) means to transmit light to the blazed reflective diffraction grating, said means including light collimating means capable of protecting the light onto a significant surface area of the blazed diffraction grating;
(c) a beam splitter receiving said light reflected from the diffraction grating;
(d) the light supplied to a wavelength monitor being transmitted through the beam splitter to the collimating means;
(e) the light reflected into the beam splitter being transmitted through the collimating means in a manner which focuses the reflected light into the beam splitter;
(f) optical sensor means to detect an unbalanced state of the light entering the beam spliter;
and
(g) the light reflected from the blaze diffraction grating being retroflected through the collimating means back to the beam splitter so that the optical sensor means detects an offaxis condition of the reflected light.

5 more elements

Dependencies are inferred from the claim text.