quantum information - Types of photon qubit encoding

How many types of qubit encoding on photons exist nowadays? I know only two:

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  Encoding on polarization:

  $$\lvert \Psi \rangle = \alpha \lvert H \rangle + \beta \lvert V \rangle$$ $$\lvert H \rangle = \int_{-\infty}^{\infty} d\mathbf{k}\ f(\mathbf{k}) e^{-iw_k t} \hat{a}^\dagger_{H}(\mathbf{k}) \lvert 0 \rangle_\text{Vacuum}$$ $$\lvert V \rangle = \int_{-\infty}^{\infty} d\mathbf{k}\ f(\mathbf{k}) e^{-iw_k t} \hat{a}^\dagger_{V}(\mathbf{k}) \lvert 0 \rangle_\text{Vacuum}$$
  
  


• 
  

  Time-bin:

  $$\lvert \Psi \rangle = \alpha \lvert 0 \rangle + \beta \lvert 1 \rangle$$ $$\lvert 0 \rangle = \int_{-\infty}^{\infty} dz\ f\left(\frac{t -z/c}{\delta t_{ph}}\right) e^{-i w_0 (t-z/c)} \hat{a}^\dagger(z) \lvert 0 \rangle_\text{Vacuum}$$ $$\lvert 1 \rangle = \int_{-\infty}^{\infty} dz\ f\left(\frac{t -z/c+\tau}{\delta t_{ph}}\right) e^{-i w_0 (t-z/c+\tau)} \hat{a}^\dagger(z) \lvert 0 \rangle_\text{Vacuum}$$
  
  

Is there anything else?