JPH0695586B2 - Light source for WDM optical communication - Google Patents

Description

TECHNICAL FIELD The present invention relates to a light source for wavelength division multiplexing optical communication used for optical communication.

2. Description of the Related Art In wavelength division multiplexed optical communication, light sources having different wavelengths are required as many as the number of multiplicities. As a light source for WDM optical communication
A light emitting diode or a semiconductor laser (hereinafter, LD) having an oscillation wavelength of 0.8 to 1.3 μm has a wavelength corresponding to each channel interval and is used.

In wavelength-multiplexed optical communication systems that have been put to practical use so far, the multiplicity is about 2 to 4 wavelengths, the wavelength interval of the light source is set to 0.1-0.2 μm interval, and the light-emitting diode or LD that becomes the light source is The desired wavelength is obtained by changing the composition / material ratio or changing the material itself.

When a light emitting diode is used as the light source, it is difficult to narrow the emission wavelength interval when the crosstalk between adjacent channels is taken into consideration because the light emitting diode has a wide spectral width of about 30 nm. In addition, when an LD with a single mode wavelength is used as a light source, the spectral width is several tens of MHz or less, so that the channels are interleaved and the multiplicity can be dramatically increased.

On the other hand, Dist-ributed with a slightly different periodic structure
In some cases, a feedback laser (hereinafter referred to as a DFB laser) is integrated on one chip to form an array.

An embodiment is shown in FIG. Five lights having different wavelengths can be obtained by the difference in the period.

Problems to be Solved by the Invention However, in the LD having the Fabry-Perot type structure which is most frequently used nowadays, even if the LDs are manufactured by the same process, the oscillation wavelength thereof varies. For this reason, in order to configure a wavelength division multiplexing optical communication system with high multiplicity, one with a required wavelength is selected from many LD samples, or
The LD having a wavelength close to the designed value is temperature-controlled to the set wavelength. For this reason, the yield of LD will be deteriorated. In addition, if the wavelength spacing is widened, the yield of LDs improves, but the power margin of the system is determined by the worst channel because the transmission loss of the optical fiber is different in each channel. The characteristics of other optical components also change. For this reason, it is necessary to change the material and structure of the channel depending on the component, which increases the cost.

In the DFB laser array shown in FIG. 7, the fabrication process is complicated, and the pitch of the grooves formed in the waveguide section must be controlled extremely precisely, which poses a serious problem in reproducibility and yield of the device. Moreover, when the LDs are driven simultaneously because the elements are arrayed, heat is generated and the temperature of the LDs rises. Therefore, the wavelength change and the output level decrease are desired.

In view of the above problems, the present invention stabilizes the oscillation frequency of LD,
A light source for wavelength division multiplexing optical communication with high multiplicity.

Means for Solving the Problems To solve the above problems, the light source for wavelength division multiplexing optical communication of the present invention includes a plurality of LDs, a plurality of LDs, a plurality of optical fibers, a plane diffraction grating, and three focusing rod lenses. And a plurality of reflecting mirrors and a light receiving element array, an external optical resonator of a specific wavelength is formed for each LD, an optical system is integrated using an optical glass block, and the power fluctuation of the 0th order diffracted light is controlled by a plane diffraction grating. It is detected and negative feedback is applied to the drive circuit of LD.

Action The present invention is intended to solve the above-mentioned problems by stabilizing the oscillation frequencies of a plurality of LDs simultaneously and independently with the above configuration.

Embodiment Hereinafter, a light source for wavelength division multiplexing optical communication in one embodiment of the present invention will be described with reference to the drawings. FIG. 2 shows a block diagram of a light source for wavelength division multiplexing optical communication in one embodiment of the present invention. Output light from the plurality of LDs 1 is input to each optical fiber 2. Each exit end of the optical fiber is arranged on the focal plane (xy plane) of the collimator lens 3. Reference numeral 4 is a plane diffraction grating having grooves cut in the Y direction. For this reason, the arrays of the optical fibers 2 must be arranged so as not to overlap in the y direction in order to avoid crosstalk between LDs. In the embodiment shown in FIG. 2, all the optical fibers 2 are arranged in the y-axis direction, but it is not always necessary to arrange them on the same x coordinate, and they may be arranged obliquely. The light emitted from the optical fiber 2 is collimated by the collimator lens 3 and is incident on the plane diffraction grating 4. Now, the plane perpendicular to the groove of the plane diffraction grating 4 (X-N plane)
When the incident angle and the diffraction angle of the light at are α and β, and the off-plane angle is φ, the light having the wavelength λ satisfies d · cosφ · (sinα + sinβ) = mλ (1). However, d is a groove interval and m is an order. if,
If the incident angle and the off-plane angle are constant, the wavelength λ of the incident light
The diffraction angle β changes as is changed. When Δβ changes, Δx ′ = Δβ · f on the focal plane of the condenser lens 5.

f is the focal length of the condenser lens 5. FIG. 3 shows the optical system when φ = 0. Output light of LD1 is optical fiber 2
After passing through the lens 3, the light is collimated by the lens 3 and diffracted by the plane diffraction grating 4. The diffracted light is condensed on the focal plane of the condenser lens 5 at a position corresponding to the wavelength. Since there are a plurality of longitudinal modes capable of oscillating in the FP type LD, if the reflecting mirror 6 is arranged at a position on the focal plane of the lens 5 corresponding to a specific wavelength, the LD 1 is externally exposed only to the specific wavelength. An optical resonator is formed. Therefore, the oscillation wavelength of LD1 is geometrically determined by the equation (1). Further, by changing the position of the focal plane of the lens 5 in the (x'-y ') plane of the reflecting mirror 6, the resonance frequency changes and the oscillation frequency of the LD1 can also be changed within the gain range. Therefore, when an LD light source that oscillates at a certain wavelength interval is required as a wavelength multiplexing optical communication light source, a plurality of reflecting mirrors 6 are arranged at required wavelength positions as shown in FIG. By arranging the emitting ends in a distributed manner in the y-axis direction, each LD1
Diffracted light of is dispersed in the y′-axis direction on the focal plane of the condenser lens 5 to form an image, and while avoiding the skirt weight of the spectrum caused by the spread of the gain of each LD 1 on the focal plane of the lens 5, The reflection mirrors 6 may be arranged two-dimensionally in the x'-y 'plane to form an external optical resonator. Fourth
The figure shows the image formation spectrum of each LD1 on the focal plane of the lens 5. One LD1 when each LD oscillates in vertical multimode
The oscillating spectrum of is dispersed and imaged in the x'direction. When the reflecting mirror 6 is arranged at the image forming point of the specific longitudinal mode spectrum, the oscillation spectrum image 7 formed on the reflecting mirror 6 is used as a light source and is returned to the LD through the original optical path again. Figure 4a,
The spectra of b, c, d, and e correspond to the emission spectra of LD1a, b, c, d, and e of FIG.

In the present embodiment, since the cat's eye optical system including the lens 5 and the reflecting mirror 6 is used for returning the first-order diffracted light at the plane diffraction grating 4, stable optical feedback can be performed.

Also, since the output light of LD1 is guided to the external optical resonator by the optical fiber 2, unlike the LD array, each LD
It becomes possible to control the temperature of 1 independently.

Further, in FIG. 5, the 0th-order diffracted light generated in the plane diffraction grating 4 is used to detect a change in the output intensity of LD1 by the light receiving element 10, and negative feedback is applied to the drive circuit 12 of LD1 to keep the output level constant. The system that has

Further, FIG. 2 shows a case where the oscillating light intensity of a plurality of LDs is controlled by using 0th-order diffracted light. In this optical system, the 0th-order diffracted light is equal to the reflected light with the plane diffraction grating 4 as a mirror,
A part of the output light of each LD 1 is imaged on the focal plane of the condenser lens 8 corresponding to the incident position of the optical fiber 2. Therefore, a light receiving element array having a light receiving surface may be arranged at a position corresponding to this image forming point. FIG. 6 shows an example of the light receiving element array.

FIG. 1 shows an integrated feedback optical system using an optical glass block. By using a condensing rod lens for each collimating lens and condensing lens, it is adhered to the end surface of the optical glass block 20 using an adhesive such as an ultraviolet curable resin. Similarly, the diffraction grating 4 is also adhered to the optical glass block 20. The output end of the optical fiber 2 that guides each output light of the LD1 is arranged and adhered to a predetermined position on the focal plane of the focusing rod lens 15, and the optical feedback mirror 6 for selecting the oscillation wavelength is used.
Arranged at a predetermined position on the focal plane of the focusing rod lens 16,
The lasing wavelength of each LD1 is selected by bonding. The 0th-order diffracted light dispersed by the plane diffraction grating 4 forms an image on the focal plane of the focusing rod lens 17, is photoelectrically converted by the light-receiving element array 18, detects the intensity fluctuation of each LD 1, and negatively affects the LD drive circuit. Return can be made. As a result, the light output intensity of LD1 is maintained at a constant value.

By integrating the optical system, mechanical stability and strength can be increased, deviation and deviation of the optical alignment due to vibration or shock can be prevented, and the overall size and weight can be reduced.

As described above, according to the present invention, three focusing rod lenses, one plane diffraction grating, an optical fiber for guiding the output light from the LD, a plurality of reflecting mirrors and a light receiving device are provided outside the plurality of LDs. It is equipped with an element array, constitutes an optical resonator with frequency selectivity outside the LD, detects the intensity change of each LD 0th order diffracted light generated by the plane diffraction grating by using the light receiving element array, and outputs it to the LD drive circuit. By feeding back, it is possible to provide a light source for wavelength division multiplexed optical communication with a high degree of multiplexing, which can stably and independently control the oscillation frequencies and output powers of a plurality of LDs.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a light source for wavelength division multiplexing optical communication in an embodiment of the present invention, FIGS. 2 and 3 are configuration diagrams of an LD oscillation control optical system in the present invention, and FIG. 4 is a focus of a condenser lens. LD on the surface
FIG. 5 is a block diagram for electrical and optical feedback control in the present embodiment, FIG. 6 is a configuration diagram of a light receiving element in the present invention, and FIG. 7 is a perspective view of a light source in a conventional embodiment. Is. 1 ... Semiconductor laser, 2 ... Optical fiber, 3 ... Collimating lens, 4 ... Planar diffraction grating, 5 ... Condensing lens, 6 ... Reflecting mirror, 7 ... Light receiving element array, 8 ... Condensing lens , 12 ... Semiconductor laser drive circuit.

Claims (3)

[Claims] 1. A plurality of semiconductor laser devices, a plurality of optical fibers for guiding the output light of the semiconductor laser devices, a focusing rod lens for collimating the output lights from the plurality of optical fibers, and the focusing rod lens. The collimated output light from the plurality of optical fibers,
The intensity of zero-order diffracted light from the plane diffraction grating that disperses in the direction according to the oscillation wavelength, the reflecting mirror that selectively returns the light dispersed by the plane diffraction grating to the emission part of the optical fiber, and the plane diffraction grating A photodetector for detection is provided, and the focusing rod lens, the plane diffraction grating, the optical fiber, the reflecting mirror, and the photodetection element are attached to an optical glass block to integrate an optical system, and the electric output of the photodetector is negative. A light source for wavelength division multiplexing optical communication characterized by returning and maintaining the output of a semiconductor laser constant. 2. The wavelength according to claim 1, wherein the optical fibers are arranged on the focal plane of the collimating lens so that the light emitted from the optical fibers enters obliquely with respect to the normal to the groove of the plane diffraction grating. Light source for multiplex optical communication. 3. An incident direction of the dispersed light selectively by using a condenser lens for condensing the dispersed light from the plane diffraction grating and a slit-shaped plane mirror arranged on the focal plane of the condenser lens. The light source for wavelength division multiplexing optical communication according to claim (1) or (2), characterized in that the light source is returned to.