JPH05107071A - Light-pumped waveguide type loop laser - Google Patents

Abstract

PURPOSE:To obtain a newly invented light-pumped waveguide type loop laser which has a signal processing circuit of signal other than pumping light source, formed by a monolithic constitution of a waveguide structure. CONSTITUTION:A loop of a loop resonance device is constituted by to straight line pats L1 and L2, and two semi-circular parts, and one L1 of the straight line parts is made to constitute a directionally coupled light wave separation part 8 to combine selectively pumping light of wave length lambdap from a pumping light source 11. The other straight line part L2 constitutes a directionally coupled light wave separation part 9 to bring out laser beam of wave length lambdas oscillated in the loop selectively to outside the loop. Open ends 101 and 102 of another end of the two light wave separation parts are tapered and made to be lean to end point thereof. An auxiliary waveguide of which dispersion characteristic of directionally coupled light wave separation is different, is also provided for suppression of unnecessary beam other than that of wave length lambdas.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is designed to couple pumping light of wavelength .lambda.p to a waveguide type loop resonator to which a rare earth element is added and extract and output an optical signal of wavelength .lambda.s oscillated by the loop resonator. The present invention relates to an optically pumped waveguide type loop laser.

[0002]

2. Description of the Related Art Conventionally, active research has been carried out to realize optical fiber amplifiers and optical fiber lasers by adding rare earth elements to the core of optical fibers, and high gain amplifiers and low threshold lasers have been realized. Came. Along with this, a ring resonator is made of an optical fiber doped with a rare earth element, pumping light of wavelength λp is coupled to the ring resonator by an optical demultiplexer, and the optical signal of wavelength λs oscillated by the ring resonator is split. Research has also been conducted on ring lasers that are taken out of the ring resonator through a wave resonator.

FIG. 4 shows a conventional example. That is, a ring resonator is made up of a panda optical fiber a containing Er and a panda optical fiber b not containing Er, and a dichroic mirror c, a bandpass filter d, a coupler e, and an isolator f are provided in the middle of the resonator. It has the inserted structure.

Here, the dichroic mirror c has a characteristic that the excitation light of the wavelength λp is reflected almost 100% and the oscillation light of the wavelength λs is transmitted with a high transmittance of 95%. Therefore, the pumping light of wavelength .lambda.p (= 1.48 .mu.m) is excited into the Er-doped optical fiber a through this dichroic mirror c. The optical signal of wavelength λs (= 1.5 μm band) oscillated by the excitation of the excitation light is taken out to the output side through the bandpass filter d and the coupler e (K. Iwatsuki, et al .: “Wavelength-Tunable Single-
Frequency And Single-Polarisation Er-Doped Fiber Ri
ng-Laser With 1.4KHz Linewidth ”, Electronics Let
ters 22nd November 1990, Vol.26, No.24, PP.2033-203
Wavelength tunable single frequency wave and single polarization Er-doped fiber ring laser with a line width of 5, 1.4 KHz, Electronics Letters).

[0005]

However, in the conventional optical fiber type ring laser, the Er-doped panda optical fiber a, the panda optical fiber b, the coupler e, the dichroic mirror c, the bandpass filter d, the isolator f, and the It consists of a pumping light source and has a very large number of parts, splice loss when connecting individual parts, and reflected light due to offset or refractive index mismatch at those connections. It is necessary to insert an isolator, it takes a lot of adjustment, assembling, and processing time to connect the respective parts, and the cost is high. Furthermore, the device configuration is plural and the size is large. Challenges remain.

An object of the present invention is to provide a novel optically pumped waveguide type loop laser in which the signal processing circuits other than the pumping light source are monolithically constructed with a waveguide structure in order to solve the above-mentioned problems of the prior art. is there.

[0007]

In order to achieve the above object, an optically pumped waveguide loop laser according to the present invention has an embedded core in which a rare earth element is added and which is covered with a clad made of a material having a refractive index lower than that of the core. Type waveguide, and the core portion is formed into a loop having two linear portions and two semi-circular portions, and one of the two linear portions is supplied with pumping light of wavelength λp from a pumping light source. A directional coupling type optical demultiplexing unit for selectively coupling into the loop, and a directional coupling type optical demultiplexing unit for extracting the laser light of wavelength λs oscillated in the loop out of the loop on the other straight line portion. The optical demultiplexing unit is provided (Claim 1). In this case, a pumping light source (for example, a semiconductor laser) may be coupled to one end of the directional coupling type optical demultiplexing unit for selectively coupling pumping light of wavelength λp into the loop ( Claim 2).

As a more preferable form, unnecessary light other than the wavelength λs is further suppressed on the output side of the directional coupling type optical demultiplexer for selectively extracting the laser light having the wavelength λs oscillated in the loop. A directional coupling type optical demultiplexing unit is provided for the purpose (claim 3). The two directional coupling type optical demultiplexing units are configured by disposing different linear cores in parallel with the two linear portions of the loop-shaped portion, and open ends of these linear cores. Is tapered to form a taper (claim 4).

The two directional coupling type optical demultiplexing sections are constructed by arranging different linear cores in parallel with the two linear sections of the loop-shaped section, respectively. Auxiliary waveguides having different dispersion characteristics are provided in parallel along these linear cores in the corresponding regions (claim 5).

[0010]

In the structure of claims 1 and 2, two linear portions L1 and L2 are positively provided in the loop-shaped waveguide, and the optical signal is demultiplexed by these linear portions, so that a narrow band pass can be achieved. Type optical filter characteristics and low loss can be achieved. The narrow band characteristic of the former is that good symmetry can be equivalently obtained when a linear core is arranged in parallel with two linear portions of a loop-shaped portion to form a directional coupling type optical demultiplexer. Further, it is considered that the reduction of the loss in the pass band is caused by the fact that the side surface is not roughened unlike the case of the curved portion because it is a straight line when the mask is drawn. In any case, the waveguide structure can be configured monolithically.

In the configuration (Claim 3) in which the directional coupling type optical demultiplexing unit for suppressing unnecessary light other than the wavelength λs is provided (claim 3), it is possible to extract the optical signal of the wavelength λs having a higher purity with good separation. Becomes Further, in the structure in which the open ends of the two linear cores are tapered and tapered (claim 4), it is possible to suppress the reflected light from the open ends from propagating in the opposite directions and coupling into the loop. it can. Further, in the configuration in which the auxiliary waveguides having different dispersion characteristics are provided in parallel along the linear core (claim 5), the optical signal having the wavelength satisfying the phase matching condition can be selectively demultiplexed.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the accompanying drawings.

FIG. 1 shows an embodiment of the optically pumped waveguide type loop laser of the present invention. This is configured such that pumping light of wavelength λp is pumped into the waveguide section 3 from the pumping semiconductor laser 11 with a coupling system to output laser light oscillated at wavelength λs in the direction of arrow 7. .. Below,
Will be described in detail.

The waveguide 12 is a buried waveguide formed on the substrate 1. The substrate 1 has a glass (for example,
SiO ₂ , or SiO ₂ , with Ge, Ti, P, B,
F, Al, Zn, K, Na, Mg, Ta, Zr, etc. containing at least one dopant), Si, GaA
Semiconductors such as s and InP, ferroelectrics such as LiNbO ₃ and LiTaO ₃ , sapphire, and magnetic substances are used. First, a low refractive index layer 2 having a refractive index of nb is formed on the substrate 1. The glass, ferroelectric, sapphire, semiconductor or the like can be used for the low refractive index layer 2. Substantially rectangular (or circular, elliptical, etc.) cores 31, 32, 33 are formed on the low refractive index layer 2.
The refractive index nw of these cores 31, 32, 33 is set to a value higher than the refractive index ns of the low refractive index layer 2. In the case of a waveguide for single mode transmission, the relative refractive index difference Δ (= (nw −n
s) / nw × 100%) is selected from the range of 0.25 to 1.5%.

Of the above cores, the core 32 has Er, N
It contains at least one rare earth element such as d, Yb, Sm, Ce, Ho, Tm. In the cores 31 and 33,
The rare earth element may be contained, but preferably it is not contained. That is, when the cores 31 and 33 contain the rare earth element, the excitation light λp and the laser light λ
This is because s is attenuated and the transmission efficiency is reduced.

As the material of the cores 31 to 33, the glass, the ferroelectric substance, the semiconductor or the like can be used. The surfaces of the cores 31 to 33 and the surface of the low refractive index layer 2 are covered with a clad 4 having a refractive index of nc (nc <nw). As the material of the clad 4, the same material as that of the low refractive index layer 2 can be used.

The core 32 is composed of two linear portions L1 and L2 and two semi-circular portions having a radius R in a loop shape.
The core 31 is a linear waveguide, and is arranged in parallel to the linear portion L1 of the loop-shaped waveguide of the core 32 with a space S1. Then, the directional coupling type optical demultiplexing unit 8 for selectively coupling the optical signal of the wavelength λp in the region of the length Lp is configured. That is, a pumping semiconductor laser 1 with a coupling system
The excitation light of wavelength λ p from 1 enters the core 31, propagates as shown by the arrow 51, and is selectively coupled into the loop-shaped waveguide 32 by the directional coupling type optical demultiplexing unit 8 and is denoted by the arrow 52. Propagate in the loop-shaped waveguide. In this case, the wavelength λp
Is selected according to the type of rare earth element contained in the loop-shaped waveguide. For example, when the rare earth element is Nd, the .lambda.p band is 0.8 .mu.m, and when the rare earth element is Er, .lambda.p is the 0.98 .mu.m band, or
The 1.48 μm band is used.

Here, the directional coupling type optical demultiplexing section 8 has a wavelength λ.
It is desirable to use a bandpass optical filter with a narrow band that selectively demultiplexes only the optical signal of p. It is configured so that the optical signal of wavelength λs oscillated in the loop is not demultiplexed. The loss in the section 8 is desired to be as small as possible in order to efficiently demultiplex.

Therefore, according to the present invention, the linear portions L1 and L2 are purposely provided in the loop-shaped waveguide 32, and the optical signal is demultiplexed at these linear portions, so that a narrow band-pass optical filter and low loss are achieved. Has been achieved.

Because the looped waveguide 32 has a radius R
If it is made up of a perfect circular waveguide, L1 and Lp will be made up of curved portions. In this case, according to various experimental results of the inventor, the bandwidth of the pass band is wide. We have found the experimental fact that the loss in the passband increases. In other words, the optical demultiplexing unit in which L1 and Lp are composed of curved portions is considered to be equivalently asymmetrical L1 and Lp,
It is considered that this widens the bandwidth of the passband. Further, the increase in the loss in the pass band is not due to a continuous side surface drawing pattern when the curved portion is mask-drawn, but is due to the side surface roughness of the curved portion which is generated when the curved portion is approximately constructed with a short straight line. it is conceivable that.

The pumping light of wavelength λp propagates in the loop-shaped waveguide 32 as indicated by the arrow 52, and the pumping light of wavelength λp is absorbed by the rare earth element in the loop-shaped waveguide 32.
Laser oscillation occurs in the loop-shaped waveguide 32. This laser oscillation oscillates at a wavelength λs peculiar to rare earth elements. For example, when the rare earth element is Nd, it oscillates in the wavelength band of 1.05 μm or 1.3 μm, and when it is Er, it oscillates in the band of 1.5 μm. The laser light having the wavelength λs oscillated in this loop is demultiplexed by the other directional coupling type optical demultiplexing unit 9, is coupled into the core 33, and is emitted from the core 33 as indicated by an arrow 7. The directional coupling type optical demultiplexing unit 9 is also configured such that the two straight line portions L1 and Ls are kept in parallel at the interval of S2 and becomes a narrow band pass type optical filter that passes only the optical signal of wavelength λs. Has been done. The bandpass optical filter does not demultiplex the optical signal of wavelength λp.

The optical demultiplexing units 8 and 9 can be realized by referring to Imoto, et al .: Waveguide type optical multiplexer / demultiplexer, IEICE Technical Report OQE87-7, 1987-04.

The open ends of the two linear core portions 31 and 33 are tapered so as to be tapered as shown by 101 and 102 in the figure. This suppresses the reflected light from the open ends 101 and 102 from propagating in the opposite directions as indicated by arrows 53 and 54, and the open ends 101
, And 102.

FIG. 2 shows another embodiment of the optically pumped waveguide type loop laser of the present invention. This is core 33
A directional coupling type optical demultiplexing unit 12 for suppressing unnecessary light other than the wavelength λs is provided on the side. As a result, it becomes possible to extract an optical signal of wavelength λs having a higher purity in the direction of arrow 7 with good separation. The optical demultiplexing unit 12 can also be realized by quoting the above-mentioned document.

FIG. 3 shows another embodiment of the optically pumped waveguide type loop laser of the present invention. This narrows the bandwidth of the band-pass optical filters of the optical demultiplexing units 8 and 9, so that the auxiliary waveguides 34 having different refractive indices and different core sizes (thickness or width) are parallel to each other along the cores 31 and 33. 35
Is provided. That is, by arranging the waveguides having different dispersion characteristics in parallel, the optical signal of the wavelength satisfying the phase matching condition is selectively demultiplexed. This can be achieved by quoting Sano, Imoto: Coupler type optical multiplexer / demultiplexer, 1987, IEICE General No.2447.

[0026]

In summary, according to the present invention, the following excellent effects can be obtained.

(1) Since the ring resonator, the optical demultiplexing section, and the input / output section are constituted by the waveguide structure, an optically pumped waveguide type loop laser having a small size and an integrated structure and a small connection loss can be obtained. Can be realized.

(2) For the above reasons, optical axis adjustment and assembly between the respective parts are not required, and mass production is possible, so that a significant cost reduction can be expected.

(3) Since the optical demultiplexing unit is composed of the directional coupling type optical demultiplexing unit consisting of two straight line portions, low loss characteristics can be realized in a narrow band.

[Brief description of drawings]

FIG. 1 is a diagram showing an embodiment of an optically pumped waveguide type loop laser of the present invention.

FIG. 2 is a diagram showing another embodiment of the optically pumped waveguide type loop laser of the present invention.

FIG. 3 is a diagram showing yet another embodiment of the optically pumped waveguide type loop laser of the present invention.

FIG. 4 is a diagram showing an example of a conventional optical fiber type ring resonator.

[Explanation of symbols]

 1 substrate 2 low refractive index layer 3 waveguide part 4 clad 7 arrow 8 directional coupling type optical demultiplexing part 9 directional coupling type optical demultiplexing part 11 semiconductor laser for excitation with coupling system 12 directional coupling type optical demultiplexing Part 31 Core 32 Loop waveguide 33 Core 51, 52 Arrow λp Wavelength of pumping light λs Wavelength of laser light L1, L2 Two straight portions R Radius of two semicircular portions S1, S2 Interval

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuyuki Imoto 3550 Kidayomachi, Tsuchiura City, Ibaraki Prefecture Hitachi Cable Ltd. Advanced Research Center

Claims (5)

[Claims] 1. A buried waveguide in which a core to which a rare earth element is added is covered with a clad made of a material having a refractive index lower than that of the core, and the core portion has two linear portions and two semicircular portions. And a directional coupling type optical demultiplexing unit for selectively coupling the pumping light of wavelength λp from the pumping light source into the loop in one of the two linear portions, and the other linear portion. An optically pumped waveguide loop laser, characterized in that a directional coupling type optical demultiplexing unit is provided in the section for selectively extracting laser light of wavelength λs oscillated in the loop outside the loop. 2. The optical pump according to claim 1, wherein a pumping light source is coupled to one end of a directional coupling type optical demultiplexing unit for selectively coupling the pumping light of the wavelength λ P into the loop. Waveguide loop laser. 3. To further suppress unnecessary light other than the wavelength λs on the output side of the directional coupling type optical demultiplexer for selectively extracting the laser light of the wavelength λs oscillated in the loop to the outside of the loop. 2. The optically pumped waveguide type loop laser according to claim 1, wherein the directional coupling type optical demultiplexing unit is provided. 4. The two directional coupling type optical demultiplexing units are configured by disposing different linear cores in parallel with the two linear portions of the loop-shaped portion, and opening the linear cores. The optically pumped waveguide type loop laser according to claim 1, wherein the end is tapered and tapered. 5. The two directional coupling type optical demultiplexing units are configured by arranging different linear cores in parallel with the two linear portions of the loop-shaped portion, respectively. The optically pumped waveguide type loop laser according to claim 1, wherein auxiliary waveguides having different dispersion characteristics are provided in parallel along these linear cores in a region corresponding to the portion.